Broken Top Loop Trail (Tr 2A.1)
The primary goal of this loop hike is to experience the fabulously diverse geology in the vicinity of the South Sister and Broken Top stratovolcanoes first hand; including ample opportunities to explore recent and ongoing glaciation, youthful silicic lava domes, basaltic cinder cones, and their associated flows, as well as the anatomy of a composite volcano laid bare on its highly dissected flanks. Use the Green Lakes Trailhead to begin and end this outing, which can be reached at mile 141.3 of Field Trip 2A. This loop hike is about 18 miles in length, and to be fully appreciated, it requires a minimum of two overnight stays; one on the north side of Broken Top at Golden Lake near the Bend Glacier, and the other in the Green Lakes area on Broken Top’s southeast flank near Crater Creek. To complete all of the day-hiking side-trips (using your overnight stops as base camps), a multi-day backpacking trip of about five days is in order. Of course, you may consider shorter options, and as this trek requires some off-the-established-trails route finding and glacier climbing, portions of it are rather strenuous and potentially dangerous, and advised against for those not in good physical condition or poorly skilled in backcountry hiking and camping. As a note of precaution, the Green Lakes area is extremely popular and heavily utilized by day-hikers, backpackers, and climbers. Try to avoid this area on weekends in late summer, and please camp only in designated locations.
The trek leaves the Green Lakes Trailhead at the northeast end of the parking area on the Fall Creek Trail; the trail follows scenic Fall Creek all the way to the Green Lakes basin, offering many opportunities for viewing beautiful waterfalls and other watery cataracts. Initially, the trail crosses the western edge of a broad, scrubby plain formed when a thin veneer of sandy-gravels were deposited by the 1966 outburst flood from the proglacial lake in the cirque on the east side of Broken Top Volcano (Nolf, 1969). Keep this in mind, if you stick with the itinerary described here, you’ll actually see the lake-source of these deposits in a couple of days. The trail crosses to the west bank of Fall Creek on a log footbridge after a few hundred yards and remains there for the next several miles. At about six-tenths of a mile, you reach the first major cataract on Falls Creek (Map 2A.20); continuing up the valley, you’ll enjoying several pretty waterfalls and a plethora of rapids, chutes, and pools as you ascend (Figure 2A.21). You pass another impressive falls at about one and a half miles; and near the two-mile mark, you reach the junction with the Moraine Lake Trail. Keep to the right to remain on the Fall Creek Trail. You can experience the Moraine Lake area on a separate backpacking trip (see the Moraine Lake Trail under this section of Optional Hiking Trails).
Figure 2A.21. One of the many lovely waterfalls and rapids on Fall Creek.
In about half a mile, the trail returns to the east bank of Fall Creek (Map 2A.20), but just before this main crossing, a simple log bridge passes over a smaller unnamed stream draining into Fall Creek from the left. This stream has its origins in several springs issuing from the base of the Miller Lava Flow a few tenths of a mile upslope. Continue climbing, the trail weaves its way upslope along Fall Creek’s right bank; in about one mile, you’ll cross a small stream (dry by late summer) and just beyond are great views of the Newberry Lava Flow across Fall Creek to the left (Map 2A.21). Looking downstream, you can see the Miller Lava Flow with Devils Hill in the background. Fall Creek has been pushed to the east side of its valley by the lava flows. These flows are associated with rhyodacitic lava of the late Holocene Devils Hill Volcanic Chain, which stretches from the Cascade Lakes highway to the northeast flank of South Sister. Devils Hill itself is the much-subdued remnant of a Pleistocene rhyolite dome, unrelated to the more recent volcanism of the Miller and Newberry lava domes and flows. The silicic volcanism portrayed by the Devil’s Hill Volcanic Chain may be an indication of South Sister’s advancing years. A silicic lava composition suggests aging of the magma chamber deep beneath the volcano, as lava of this type is normally erupted in the latter stages of volcanism associated with a given magmatic source. It may also indicate enrichment of the magma chamber with melt from a different, more felsic source. These youthful lavas partially blocked the upper Fall Creek drainage to form the Green Lakes. Subsequent infilling of the lake basin by slope wash and mass wasting has divided the original lake into one large and three smaller lakes.
Not much further up the trail (at a point upstream of the lava flow constriction), the valley floor suddenly flattens out, Fall Creek becomes placid, and your first good views of South Sister’s eastern flank begin to open up (Figure 2A.22). Notice the coarse, blocky surface and grayish, fine-grained rhyodacite and glassy pumice and obsidian of the Newberry lavas; these features attest to the erupted magma’s relatively low temperature, high water and silica content, and high viscosity. Continue hiking, in about half a mile you pass a sign indicating that you have entered the Green Lakes Use Area.
Figure 2A.22. Fall Creek, not far from its Green Lakes outlet; Newberry Lava Flow, part of the silicic Devils Hill volcanic chain on its left bank with South Sister in the background.
You reach the first of two closely spaced trail intersections about four and four-tenths of a mile from the Green Lakes Trailhead at the margin of the Green Lakes basin, just before reaching the first of the lakes (Map 2A.21). The left-hand trail leads to a climber’s route to the summit of South Sister (save this for the Moraine Lake Trail described later), while the right one is marked with a sign for Park Meadows (this trails heads over Green Lakes Pass and into the Whychus Creek watershed and is the route you wish to take). In a few short steps, another trail junction greets you; continue straight (left) around the east side of the largest of the Green Lakes, the right-hand trail is marked Soda Creek (you’ll return this way in a few days). The trail you are now on brings you across a broad flat covered in fine silicic tephra by following the north shore of a small lake.
Yet another trail merges from the south in about two-tenths of a mile (Map 2A.21). Continue northeast around the east side of the largest lake, the views of South Sister and the late Holocene silicic volcanics of the Devils Hill Volcanic Chain are quite pleasing. In about nine-tenths of a mile, the trail crosses the outlet stream from the uppermost of the Green Lakes, passing from a tephra covered ridge to the toe of a fresh, bouldery alluvial fan that you can see sweeping up the valley before you. Shortly, you pass back onto a older tephra coated ridge; the youthful alluvial fan remains to you immediate left as you climb this ridge. In roughly four-tenths of a mile, a sign indicates that you are leaving the Green Lakes use area. Continue ascending the ridge, you’ll reach Green Lakes Pass in another six-tenths of a mile (Map 2A.21). Be sure to look carefully across the valley to your left. The alluvial fan deposits you followed earlier can be traced into debris flow levees bordering a fresh-looking channel at the fan head (Figure 2A.23). Following these levees upstream, the source of the alluvial fan and levees is easily traced to a light gray stream channel notching a bouldery neoglacial moraine high on the eastern flank of South Sister. Catastrophic downcutting into the moraine from a proglacial lake outburst flood appears to have produced the bouldery debris. Green Lakes Pass itself offers great views to the southeast of Broken Top Volcano and back to the west of South Sister Volcano; compare the degree to which each peak is scoured by erosion, it is not difficult to see that Broken Top is the older of the two composite volcanoes.
Figure 2A.23. The head of an alluvial fan lies in the foreground, its axis occupied by a fresh-looking stream channel bordered by debris flow levees; beyond it neoglacial moraines on South Sister’s eastern flank exhibit signs of catastrophic erosion, the likely source of the deposits.
Beyond the pass (by some 200-250 yards), you pass several outcrops of andesite on the right side of the trail that are smoothed and polished by the passage of ice. Take a few moments to examine the scoured bedrock surfaces, these classic polished whalebacks (rouche mountonee), scared by glacial striations (Figure 2A.24); note their alignment relative to their position near the pass, a substantial ice mass occupied the divide area, flowing outward and downward into the Whychus Creek and upper Deschutes River drainages.
Figure 3.2A.24. Whalebacks near Green Lakes Pass, beautifully polished and striated by the passage of ice.
As you approach six-tenths of a mile beyond the pass, watch carefully on your right side for a faint trail heading toward Broken Top’s north face (Map 2A.21); this is the trail to Golden Lake, your first night’s camping destination. Assuming you have successfully found this faint trail, follow it downslope (it is pretty obvious where the trail is going) and into the upper end of a meadowed stream valley. The steep slopes will begin to hedge you in; walk east and slightly north until you reach Golden Lake at the foot of a north trending ridge that forms the eastern perimeter of valley. If you enjoy solitude, and serene mountain splender, Golden Lake is for you, with its grassy meadows and wide-open views of Broken Top to the southeast, South Sister to the west, and both Middle and North Sister to the northwest. The sunset view of Broken Top’s sheered-off north face from the shores of Golden Lake is fantastic (Figure 2A.25). Glacial erosion has sliced deeply into the mountain’s roots here, exposing near vent lava flows and volcanic breccias intruded by multiple feeder dikes. The long ridge to the northwest of Broken Top’s summit cone is held up by resistant rhyolite, exposing a portion of the peak’s early Pleistocene foundation. Neoglacial moraines cling to Broken Top’s northeast side, holding in the remnants of the Bend Glacier.
Figure 2A.25. Broken Top Volcano’s glacially scared northern face (as seen from Golden Lake).
Start your day with a marvelous sunrise on South Sister from Golden Lake’s east shore (Figure 2A.26). When you are ready to proceed, cross Golden Lake’s outlet stream and make for the inlet stream on its southeastern shore. A well established climber’s route ascends the ridge along the inlet stream (Map 2A.21). Follow this trail (and stream) upslope for about three-quarters of a mile; when the stream bifurcates, take the obvious trail up the steep slope to the left. Topping the bouldery ridge brings you to the shores of a small lake, hemmed in by the moraine you’ve just ascended. These glacial deposits are likely age equivalent to the late Pleistocene Canyon Creek advance of Scott’s (1977) Cabot Creek glaciation. Continue around this small lake and to another just upslope. At this point, the route you’ve been following more or less disappears into the boulder fields and meadows of this alpine environment; a topographic map and/or GPS would help greatly, especially if your bushwacking skills are a bit lean. Work your way around this lake to the left and head east over a broad, low ridge; you should soon arrive at a small perennial stream. A Canyon Creek glacier extended down this valley several tenths of a mile to the north in the latest Pleistocene.
Figure 2A.26. Sunrise on South Sister from the inlet stream on Golden Lake’s east shore.
From this location, continue hiking eastward, keeping just above the tree covered slopes (Map 2A.21). You’ll cross several rocky ridges with intervening grassy meadows and lazy little streamlets draining from perennial snowbanks and the remnants of the Bend Glacier. Great views of South Sister lay behind you. In the height of summer, these watery meadows are alive with flowers; and are dotted with the occasional boulder that has rolled down from the weathered face of Broken Top just to your right (Figure 2A.27). Just upslope from your meadowed path are obvious fresh, bouldery neoglacial moraines (the Canyon Creek moraines are well down slope to your left). In just over one mile from the last lake, after you have crossed your fourth ridge, you’ll arrive at a larger stream draining directly from the Bend Glacier (Map 2A.21). This is the head of Whychus Creek. Cross to the east side and find a good place to stow your backpack for a bit. From here, climb upslope along the stream and then onto the obvious moraine crest immediately to your left for an eye-popping view of Broken Top Volcano’s northeast face and what remains of the Bend Glacier (Figure 2A.28); it’s a mere six-tenths of a mile round-trip. The Bend Glacier has melted back considerably from its former, Little Ice Age maximum, the end moraines deposited during that late Holocene neoglacial event are well preserved. In fact, you are standing on one segment of that former glacier’s right lateral moraine. Look across the small stream valley to your west, and you can trace the left lateral moraine’s crest up and further to the right from near your crossing point of the stream. In the valley below the glacier, notice the molded and streamlined ground moraine formed by flowing ice at the former glacier’s bed. Your perch is also superbly located for intimate observation of Broken Top’s volcanic stratigraphy. The headwall above the Bend Glacier exposes Broken Top’s vent, marked by a jumble of faulted and deformed volcanic breccias intruded by small mafic to intermediate plugs that feed the former volcano’s eruptions. To the right is a textbook layer cake of sloping lava flows and pyroclastic deposits intruded by small basaltic feeder dikes. Return for your backpack at your leisure and carry on.
Figure 2A.27. A large boulder comprised of volcanic breccia tumbled from the north face of Broken Top makes for a picturesque location as well as a geologically interesting one; the stratified volcanic breccia is typical near-vent pyroclastic material associated with the intermediate volcanism of with composite volcanoes.
Figure 2A.28. Broken Top’s jaggedly exposed northeast face, what’s left of the Bend Glacier at its feet.
Once back at your stream crossing point, head north and east around the prow of the ridge on your right-hand side (Map 2A.21). This ridge and much of the higher slopes just beyond are comprised of Pleistocene andesites, more of Broken Top’s older foundation. Round the base of the ridge, and begin ascending toward its crest from the much gentler eastern side (Map 2A.22). After somewhat less than one mile, you should arrive at a vantage point on the ridge crest about midway to the summit, here comprised of frost-shattered platy andesite; this location is ideal for looking westward along the cliffs making up Broken Top’s north flank (Figure 2A.29). The entirety of the Bend Glacier is easily observed tucked within a cirque recessed into the volcano’s northeast face. Note the crevasses marring its surface, an indication that the glacier is still flowing, alive despite its unhealthy state. The glacier’s former Little Ice Age glory can easily be reconstructed by connecting an imaginary line from the crest of moraines to the right of its terminus to the top of the perennial snowbanks above (and now detached from) the glacier’s head. Look carefully at the cliff above the glacier to see a beautiful example of a basaltic dike intruding upward through interbedded lavas and pyroclastics (Figure 2A.30). The lava flows are uniformly down-sloping dark sheets sandwiched between reddish, oxidized layers of pyroclastic units; the dike intrudes diagonally upward from the shadowy cleft in the cliff face to where it juts into the sky as a resistant pinnacle. This is a classic exposure of the composite nature of a stratovolcano’s volcanic stratigraphy.
Figure 2A.29. The Bend Glacier in its current state lying at the head of a cirque cut into Broken Top Volcano’s northeast flank.
Figure 2A.30. The cliff above the Bend Glacier exposes textbook interbedded lava flows and pyroclastic deposits intruded by a mafic dike; South Sister lies behind and to the right.
Now make for the ridge summit above you, a mere four-tenths of a mile away (its all downhill from there!) (Map 2A.22). The upper portion of the ridge is formed of near vent deposits, a breccia of welded volcanic bombs, rock fragments, and lapilli cinders; and as you climb, you pass several vertically oriented basaltic dikes. The summit makes an inviting lunch stop and a fabulous place to look around. First, look upward at Broken Top’s summit and upper slopes for a graphic display of the internal stratigraphy of a stratovolcano. In particular, look for the basaltic feeder dikes intruding the layer cake of near vent volcanic breccias and pyroclastic deposits on its northeast face. To the north and west, your view takes in the Whychus Creek watershed, with the Three Sisters marching off in the distance (Figure 2A.31). In the foreground, the full arry of the Bend Glacier’s late Holocene Little Ice Age end moraines and late Pleistocene Canyon Creek moraines spread out before you. Now look to the south into the cirque basin on the northeast face of Broken Top Volcano (Figure 2A.32). A perennial snowfield still clings to the lower headwall, dipping its icy feet into a gorgeous little proglacial lake dammed by neoglacial moraines deposited during the Little Ice Age; Mt. Bachelor and Tumalo Mountain appear on the skyline.
Figure 2A.31. The Whychus Creek watershed, bordered on the south and west sides by Broken Top Volcano and the Three Sisters; neoglacial and Canyon Creek moraines are clearly visible beyond the compound cirque headwall on Broken Top’s north face.
Figure 2A.32. The cirque on Broken Top’s eastern face, containing a proglacial lake encircled by late Holocene neoglacial moraines deposited during the Little Ice Age.
From the summit, it is a comparatively easy hike on an established climbers route down to the east shore of the proglacial lake below; and from there, walk along the stream as it exits the lake through a narrow slice cut deeply into the neoglacial terminal moraine six-tenths of a mile ahead (Map 2A.22). The notch carved through the moraine is the source of the outburst flood deposits seen on the Fall River Trail near the beginning of this trek (Nolf, 1969). Imagine the turbulent, rushing waters of this creek catastrophically downcutting through the till piled here, literally overnight, and carrying much of it down to Sparks Meadow about five miles away. The likely cause was simple, once enough water had accumulated in the proglacial lake basin at the foot of the glacier, it began flowing over the moraine crest at the lowest point of passage. The escaping water gathered energy as it flowed downslope, the energy provided the force to entrain the loose till of the moraine, and catastrophic entrenchment ensued. Only when the stream had cut headward and downward completely through the moraine to establish a much more gentle gradient to its channel did the energy conditions decrease sufficiently so that the flowing water could no longer carry its load. The outburst flood was over.
Once through the moraine, head downstream to your left; you will likely encounter several choices of trail, but all routes lead downslope. After about half a mile, cross all stream channels to your left and pass through a low saddle on the ridge descending Broken Top’s southern flank (Map 2A.21); Mount Bachelor lies ahead in the distance, its symmetry and unblemished slopes belay its youth. Now walk down the stream valley, passing Ball Butte’s highly scoured edifice on the left; multiple lava flows are exposed in the butte’s left flank. The fresh, bouldery debris strewn along the stream course between you and Ball Butte are the telltale remnants of the outburst flood described earlier. The route continues downslope three-quarters of a mile, descends a steep ridge, and abrupt crosses onto a broad flat covered in small pumice lapilli from the now distance Rock Mesa eruption. Look to the northwest for a great view of Broken Top’s bisected summit, the central portion of its southern flank completely gouged away by a large cirque (Figure 2A.33). The remnants of the Crook Glacier peek from behind a wall of neoglacial debris perched at the outer edge of the cirque basin. Just ahead, several shallow, dry, debris-strewn channels traverse northeast to southwest across this flat, cut by the outburst flood. Your climber’s route soon crosses Soda Creek and in a quarter mile it merges with the main Broken Top Trail coming in from the southeast (Map 2A.23). A sign indicates you are near the Three Sisters Wilderness boundary.
Figure 2A.33. A picture-perfect view of Broken Top’s southern flank; the cirque basin deeply dissecting its center preserves the remnants of the Crook Glacier behind a screen of neoglacial debris, in the foreground a boulder-strewn dry channel recently scoured by a proglacial lake’s outburst flood.
Head northwest on the Broken Top Trail toward the Green Lakes basin; the last leg of the day’s hike takes you the rest of the way around Broken Top Volcano to tie the knot in your circumnavigation. Note the sharply contrasting landscape on this sunny side of the volcano. The slopes are much more open, dotted with small stands of subalpine fir and Douglas fir, and blanketed with a thin layer of Rock Mesa pumice. Cross Soda Creek in about 500 feet and hike downslope into the valley of Crater Creek; great views of Broken Top’s southern, ice-sculpted slope abound. In about half a mile, the trail crosses an irrigation ditch which captures much of the water from Crater Creek (Map 2A.20). A climber’s route heads upslope along the ditch to join Crater Creek and continues into the Crook Glacier’s cirque basin. Another trail leads south along the ditch to join Forest Service access roads outside of the Three Sisters Wilderness and the Broken Top Trailhead. Continue west on the Broken Top Trail, first crossing two branches of Crater Creek itself, and then passing just upslope of several perennially flowing springs about four-tenths of a mile beyond the ditch (Map 2A.20). The riparian vegetation and sparking water of the springs look quite inviting as you traverse these open, radiant, pumice-strewn slopes.
Six-tenths of a mile further, the Todd Lake Trail joins you from the south (Map 2A.20); remain on the Broken Top Trail. Shortly, you begin rounding the southern flank of the early Holocene Cayuse Crater cinder cone and are offered views to the southwest of Sparks Lake and the uppermost portion of the Deschutes River valley. Notice the contrasting reddish, basaltic scoria comprising this cinder cone. In about half a mile from the Todd Lake Trail junction, you pass through the breach and gutter system on Cayuse Crater’s southwest side, the source of the mafic Cayuse Lava Flow described at mile 135.7 of Field Trip 2A. Another six-tenths of a mile brings you to one of the few perennial streams on this drier side of the mountain, a tributary to Fall Creek (Map 2A.21). At the far edge of this valley, be sure to look back the way you came for a good view of the Cayuse Crater cinder cone and Mount Bachelor in the distance (Figure 2A.34). Your destination isn’t far now. Continue wrapping northwest around Broken Top’s lower slopes; about half a mile takes you around a major spur ridge descending Broken Top’s southwest flank (remember this location, you’ll be returning here tomorrow). From there, it’s about another mile to your campsite. You’ll pass through two small, dry stream valleys on the way, and just beyond the second valley, you encounter the now familiar Green Lakes Use Area sign. Cross a perennial stream in a couple hundred yards; the gorgeous little meadow here affords a wonderful view of Broken Top’s west side (Figure 2A.35). Start looking for a campsite (Map 2A.21) so you can come back for a sunset; there are two nice sites on the north side of this little stream valley. Incidentally, these campsites offer easy access to marvelous South Sister sunrises from the shore of the southernmost of the Green Lakes (Figure 2A.36); but are well away from the more crowded sites closer to the lakes.
Figure 2A.34. Cayuse Crater, an early Holocene basaltic cinder cone, sits perched on the southwestern flank of Broken Top Volcano; Mount Bachelor can be seen in the distance to the right of Cayuse Crater.
Figure 2A.35. A beautiful perennial stream and meadow on Broken Top’s western slope offer great camping nearby, easy access to the Green Lakes without the crowds; and who can beat the view?
Figure 2A.36. A well-deserved sunrise on South Sister Volcano from the eastern shore of the southernmost of the Green Lakes.
Today you can take it “easy” with a short climb to Broken Top’s southwestern summit (Map 2A.21). To begin your trek, hike about a mile back on the Broken Top Trail to that southwest trending spur ridge mentioned yesterday. Look for a grassy area above and below the trail (where the sun first comes over the ridge in the morning). Head off-trail here and upslope to your left. Soon you’ll break out of forest cover onto pumice lapilli covered slopes; just keep to the ridge. In about seven-tenths of a mile, you reach a segment of the ridge comprised of frost-shattered, platy rhyodacite. The ridge seems to be held up by this lengthy spine of dense, resistant bedrock, an exposed portion of Broken Top’s more silicic foundation (Figure 2A.37). Continue hiking along the ridge, the views are inspiring and your goal is obvious.
Figure 2A.37. Broken Top’s southwestern spur ridge, your route to the top; note the break in slope in the middle distance, the ridge below is comprised of rhyodacite, the ridge above is comprised of basaltic andesite lavas, volcanic breccia, and dikes.
The ridge steepens significantly in about half a mile (Map 2A.21). Take careful note of this location, a low ridge running diagonally downslope to the northwest form here will serve as your route back when you return from the summit. Continue upslope and to the right of several large outcroppings of basaltic andesite lavas. You are now climbing Broken Top’s much eroded summit cone. In about two-tenths of a mile, you pass the first of many excellent outcrops of basaltic andesite feeder dikes intruding near vent volcanic breccias. Not far ahead, an excellent outcropping of bedrock exposes the steeply angled basaltic andesite dike intruding volcanic breccia (Figure 2A.38). Briefly climb carefully onto the dike itself for spectacular views across the valley of Fall Creek to South Sister and the silicic vents of the Devils Hill Volcanic Chain on its nearer southeast side; the rhyodacitic ridge you ascended during the first part of this morning’s climb can easily be seen running away southwest from your position.
Figure 2A.38. A basaltic andesite feeder dike intrudes near vent volcanic breccias; note the reddish “baked” zone where the dike lies juxtaposed against the volcanic breccia.
As you approach the top, make your way over to the saddle in the ridge just south and downslope of the summit for your first view into the cirque basin cut deeply into Broken Top’s southern flank. The remnants of the Crook Glacier lie directly below, encircled by its Little Ice Age end moraine (Figure 2A.39). Now for that final push to Broken Top’s southern summit; watch your step on this final ascent, the volcanic breccia makes for loose footing. You have come over half a mile up this steeper portion of the ridge (Map 2A.21). All of your hard work has not been for naught; brace yourself for one of the most astounding views in all of the Oregon Cascades (Figure 2A.40). Looking to the west and north, the spectacular Three Sisters stratovolcanoes march in a line; their height and massive bulk dwarfs everything else along the nearer portions of the Cascade Crest. South Sister dominates this perspective, so much so that it seems fairly obvious which sibling got all of mother’s attention. North Sister seems frail by comparison, and indeed she is the elder sister, much more heavily dissected by age and the work of glacial erosion. In the nearer view, one can see the youthful, late Holocene silicic domes and flows of the Devils Hill Volcanic Chain beginning on South Sisters southeast flank with the largest (the Newberry Flow), then stretching to the south and shrinking in size with each new vent. And lying directly at the base of South Sisters eastern slope are the blue-green jewels of the Green Lakes, their color in sharp contrast to the grey slopes above. Your Eagle’s Eyre occupies a narrow slice of ridge on Broken Top’s slightly lower southern summit and lies atop a layer cake of steeply outward dipping lava flows and pyroclastic deposits that form the western flank of the highly dissected summit cone, a many-hued stratigraphy as only a classic composite volcano of this caliber should exhibit (Figure 2A.41).
Figure 2A.39. The Crook Glacier, nestled within its Little Ice Age end moraine, as seen from near Broken Top’s southern summit.
Figure 2A.40. The Three Sisters volcanic platform as seen from Broken Top’s southern summit; a finer view cannot be found in the Oregon Cascades.
Figure 2A.41. The highest point on Broken Top Volcano lies atop a layer cake of lava flows and pyroclastic deposits that form the western flank of the highly dissected summit cone; as observed from the volcano’s slightly lower southern summit.
When you can tear yourself away from your contemplations, the reality of your descent back to camp will sink in. Use caution on the loose scree as you climb down that long ridge. When you reach the break in slope and are back on rhyodacite at just over six-tenths of a mile below, look for that low ridge descending diagonally to the right away from your position (Map 2A.21). Work your way down this pumice-blanketed ridge and to the right into and across the broad bowl-depression below. Cross first one dry stream channel, traverse over a low ridge, and then cross a second dry stream channel. Follow the course of this second stream downslope until it merges with a perennial stream; you have come just over a mile from the rhyodacitic ridge. This stream is the one flowing near to your campsite; it issues from springs located a few hundred yards upvalley from the confluence with its seasonally dry tributary.
Cross the right bank of the stream and continue hiking downvalley about four-tenths of a mile until your reach the familiar Broken Top Trail (Map 2A.21); your campsite is a mere couple hundred yards away.
Do as you please this afternoon; after that climb, you deserve a rest. Consider a leisurely stroll to the shores of the largest of the Green Lakes, August afternoons are normally perfect for taking in a swim.
Sleep in; today you have only to return to the Green Lakes Trailhead (or, on second thought, would you care to see another sublime sunrise from South Green Lake before you go?). It isn’t a complicated path; from your campsite, return to the Broken Top Trail and head downslope into the Green Lakes basin. In a few hundred yards you arrive at your first trail junction. The right fork heads around the east side of South Green Lake, a shortcut toward Green Lakes Pass; the left fork (the one you want) makes for the Fall Creek Trail. Hike another two-tenths of a mile to your next trail junction (Map 2A.21). Make a left turn here and almost immediately, a third trail junction appears. Turn left at this junction and you are on the Fall Creek Trail heading south and downslope all the way to your waiting vehicle, after your recent accomplishments, a relatively breezy four and a half miles ahead.
Moraine Lake Trail (Tr 2A.2)
This loop hike is about nine miles in length, but with several miles of additional side trips possible. It is intended to be an overnight backpacking excursion at the very least, with a stay at Moraine Lake an absolute must; but it should be expanded into a trip of several days with time and a desire to include a pilgrimage to the summit of South Sister Volcano. Much of the hiking is on well-defined trails and climbing routes, with only a brief bit of off-trail scrambling on a day-hiking option in the vicinity of Le Conte Cone and Rock Mesa. As a note of precaution, the Moraine Lake area is extremely popular and heavily utilized by day-hikers, backpackers, and climbers. Try to avoid this area on weekends in late summer, and please camp only in designated locations.
The fantastic views from the top of Oregon’s second highest volcanic edifice are reason enough to complete this trek. However, the real goal of this backpacking trip is to provide a brief snap-shot into the geological diversity of South Sister Volcano, one of the finest representatives of a composite volcano to be seen anywhere. The trip includes ample opportunities to explore recent and ongoing glaciation, a nearly perfect example of a basaltic cinder cone, youthful silicic lava domes and their associated flows and pyroclastic ejecta, and the composition and construction of South Sister stratovolcano herself.
The trek leaves from the Green Lakes Trailhead at the northeast end of the parking area on the Fall Creek Trail; the same location as for the Broken Top Loop Trail (see the Broken Top Loop Trail under this section of Optional Hiking Trails) (Map 2A.20). The trail follows scenic Fall Creek for the first two miles and begins by crossing the western edge of a broad, scrubby plain formed when a thin veneer of sandy-gravels were deposited by the 1966 outburst flood from the proglacial lake in the cirque on the east side of Broken Top Volcano (Nolf, 1969). The trail crosses to the west bank of Fall Creek on a log footbridge after a few hundred yards and remains there for the next several miles. At about six-tenths of a mile, you reach the first major falls on Falls Creek; continuing up the valley, you’ll enjoy several pretty waterfalls and a plethora of cataracts, chutes, and pools as you ascend (Figure 2A.21). You pass another impressive falls at about one and a half miles; and just past the two-mile mark, you reach the junction with the Moraine Lake Trail. Veer left here onto the trail headed for Moraine Lake.
After another eight-tenths of a mile, the trail traverses the northern end of a rhyodacitic lava flow associated with a small silicic dome (Map 2A.20), one of several lava domes and flows that make up the late Holocene Devils Hill Volcanic Chain (Taylor et al., 1987). Notice the jagged, blocky nature of this flow (Figure 2A.42), indicative of very viscous, silicic lava that didn’t flow far from its vent. At three miles from the trailhead, you cross the oft-dry channel of Goose Creek (Map 2A.24), a brief opening up valley offers a glimpse of South Sister. Goose Creek usually flows only during the spring snow melt season.
Figure 2A.42. The margin of a rhyodacitic lava flow; its rough, blocky exterior is typical of high viscosity, silicic lavas.
When you reach three and two-tenths miles, a trail sign indicates that you are entering the Moraine Lake Use Area; within this area, you are allowed to camp only in designated camp sites. Another three-tenths of a mile brings you to a trail junction (Map 2A.25) marked by a sign directing you back to the Green Lakes Trailhead and forward to the Devils Lake Trailhead and South Sister climbing routes. This junction offers your first view of Moraine Lake and lies near the Goose Creek outlet of the lake. At this point, it should be noted that Moraine Lake’s name is a misnomer, there is no moraine encircling Moraine Lake. Much of the area surrounding the lake is underlain by basaltic andesite flows issued from South Sister Volcano, although a blanket of near vent rhyodacitic pyroclastic deposits of varying thickness coats much of the bedrock (Taylor et al., 1987). The pyroclastics were ejected from the late Holocene Rock Mesa lava dome west of Moraine Lake. Patchy ground moraine from late Pleistocene glaciation of the area probably lies beneath the tephra.
Multiple campsites are located on the ridge immediately south of the trail junction nearest the lake, but for a bit more seclusion, follow the side trail north across the Goose Creek outlet. The trail remains at the eastern edge of a broad plain covered in silicic tephra (some pumice fragments are fairly sizable) This plain probably once covered by the waters of Moraine Lake prior to dissection at its Goose Creek outlet. In a couple hundred yards, a very nice campsite can be found just upslope in the trees (Map 2A.25). This base camp offers several worthy day-hiking opportunities.
Assuming that you got an early start on your hike up to Moraine Lake, you’ll still have plenty of time for some exploring. We’ll start with a warm-up hike in the afternoon to Little Broken Top (about five miles round-trip), a wonderful example of a small silicic lava dome overlooking the much larger Rock Mesa rhyodacite dome and flows. This dome is the southernmost of several small rhyolite domes and a 400-meter-long series of vents clustered along an inferred graben about three-quarters of a mile northeast of the summit of Rock Mesa. Together, Rock Mesa and these smaller fissure vents and silicic domes were the source of two significant late Holocene tephra plumes examined near Devils Lake at mile 133.1 of the road log for Field Trip 4A. Little Broken Top and its partners were erupted just prior to the much larger Rock Mesa event based on the stacking of tephras from these vents (Figure 2A.17).
To begin your day-hike, return to the trail junction and sign near the Goose Creek outlet from Moraine Lake. Head southwest around the shore of the lake, and climb the valley at its end out of the lake basin; in four-tenths of a mile, you reach a trail junction (Map 2A.24). Take the right-hand trail, a short cut to the main climber’s route to the summit of South Sister. In just over three-tenths of a mile further, you’ll reach the main route coming in from the south (this route merges with the Hell Creek Trail out of the Devils Lake Trailhead); turn right and head up slope (Map 2A.25). You have ascended onto a wide, elongated ridge cored by basaltic andesite extending southward from South Sister’s summit cone. The ridge is strewn with a thick blanket of pyroclastic material from the Rock Mesa eruption; note the size of clasts has increased as you get closer to the source vent. This ridge stroll affords great views of South Sister (Figure 2A.43) and Moraine Lake. It may serve as a fine alternate destination and offers an especially scenic sunset view of Moraine Lake with the Devils Hills silicic lavas and Broken Top Volcano as a backdrop (Figure 2A.44).
Figure 2A.43. South Sister Volcano from the climber’s route on the ridge above Moraine Lake.
Figure 2A.44. Moraine Lake, with the silicic lavas of the Devils Hill Volcanic Chain just beyond and Broken Top Volcano as a backdrop (Is a finer sunset vista possible?).
If Moraine Lake hasn’t captured your attention, continue your gradual, undulating ascent of the ridge. Nine-tenths of a mile from your last trail junction brings you to the head of a small drainage off to your left (the first discernable drainage on the left side of the ridge) and an abrupt steepening of the trail where the ridge narrows (Map 2A.25). This is your signal to head off-route to your left. Your goal should be easy to spot, the silicic lava dome called Little Broken Top lying on a ridge across the drainage and somewhat downslope of your current position (Figure 2A.45). It is roughly a one mile to hike over to its base, circle its perimeter, and return to this point. Little Broken Top is a nearly symmetrical, perfectly formed example of a silicic dome; when you reach its base, note the jagged, blocky nature of the viscous, silicic lava that barely flowed from the vent area. Be sure to walk around to the dome’s western side, or better yet, climb carefully to the top of the lava dome for an amazingly intimate view down onto nearby Rock Mesa, a much larger silicic dome and flow you’ll visit on another hike.
Figure 2A.45. Little Broken Top, a small, nearly conical silicic lava dome (on the left) paired with its much larger eruptive twin, the Rock Mesa silicic dome and flow (in the background on the right).
This is a fortuitous location to consider the generation of lava domes and their associated flows and tephras. The Rock Mesa Flow and its associated widespread tephra deposits (as well as the silicic dome and vents behind you) resulted from the most recent episode of volcanism on South Sister Volcano erupting roughly 2,000 years ago (Scott, 1987; Scott et al., 1989; and Scott and Gardner, 1990). These rhyolitic volcanic eruptions occurred in two stages: 1) an initial stage of gas-rich, explosive eruptions from several aligned vents fed by dikes or segments of a single dike emanating from the same magma source that produced immense clouds of pyroclastic debris that blanketed the southern flank of the volcano and nearby areas with a pumiceous, air-fall deposit which may have been accompanied by localized pyroclastic surge deposits; and 2) feeder dikes were locally enlarged along the dike lineaments, enhancing magma supply to these locations, which became the principal conduits for the eruption of silicic, degassed magma from the vents that generated Little Broken Top and the Rock Mesa Flow. Presumably, the size of the feeder dike and volume of magma it produced is expressed by the surface dimensions of the individual rhyodacitic lava domes and flows. Figure 2A.17 shows the distribution of tephra deposits produced by the Plinian style eruption plumes from these vent sources (Scott, 1987).
The surface of the Rock Mesa Flow is an incredibly irregular mix of heaped-up mounds of rough, angular blocks of glassy obsidian, pumice (frothy glass), and rhyodacite. On first impression, the mounds seem to be formed randomly, but careful observation reveals a pattern of distinctly arcuate ridges that parallel the margins of individual flow lobes; the result of deformation of the rapidly cooling and solidifying rock of the flow surface by the hot, plastic, still-flowing rock of the lava’s interior. They form perpendicular to flow, and thus indicate the rhyolitic lava’s flow direction (generally away from the vent and downslope). Silicic flows like this one often develop distinctive vertical and lateral zonation (Fink, 1983; Fink and Manley, 1987; Manley and Fink, 1987; and Metz and Bailey, 1993). The flow surface forms as a fine, vesicular, light-colored volcanic breccia that becomes broken up by continued movement within the flow. As the flow spreads downslope, its leading edge continually buries previously formed breccia as a basal layer beneath the flow. This surficial carapace grades inward to a zone of denser, more glassy, but coarsely vesicular pumice and obsidian, which in turn grades inward to a finely crystalline rhyolite core. Zonation can be distorted at the flow margins by compression of the flow that causes complex faulting, folding, and ramping.
Highly siliceous magma is an extremely viscous material that must be quite thick in order to flow. The viscous nature of this magma reduces the mobility of ions and prevents chemical bonding and the formation of mineral crystals. This results in the formation of a natural glass that can contain considerable gas bubbles, forming obsidian and a range of pumice types. These compositional variations are exhibited in the large obsidian and pumiceous blocks that comprise the flow’s surface, generally concentrated into ridges on the flow surface, as seen from your elevated position.
If you’ve seen and experienced enough for the moment, return to the main climber’s route and head back to your camp site at Moraine Lake, but you may wish to linger on the ridge for that inspiring sunset.
Now for the main event of this backpacking excursion; summiting South Sister! Rise early for a spectacular sunrise at Moraine Lake (Figure 2A.46) and to beat the daily pilgrimage crowding the climber’s route to South Sister’s crown. Return to the trail junction with the main climber’s route up South Sister’s southern flank at about three-quarters of a mile (Map 2A.24). Ascend the long ridge above Moraine Lake to the point where you left it yesterday; occasional outcrops reveal the ridge’s andesite composition, but much of it is covered in loose pumice lapilli, small volcanic rock fragments, and silicic ash erupted from late Holocene silicic vents related to the Rock Mesa eruptions that you examined yesterday. A quick climb up the west side of the narrowing ridge from here brings you two miles from camp and to a trail junction with the now closed Canyon Trail, a former climbing route coming up directly from Moraine Lake (Map 2A.25).
Figure 2A.46. One of any number of gorgeous sunrises to be enjoyed from the shores of Moraine Lake; South Sister Volcano lies to the right.
Continue upslope; be sure to pause often and look around, the views really begin to open up to the southward. About mid-way to the top (you have now come three miles from camp), the trail passes through bouldery glacial till from the Little Ice Age moraine of the Lewis Glacier and soon crosses the moraine’s crest, passing around the west side of the glacier’s modern remnants. The modern Lewis Glacier clings precariously to South Sister’s southeast flank, a vulnerable sunny position that must be receiving abundant wind-drifted snow from the west in order to counter the glacier’s high rate of summer melting. A climber’s route merging from the right connects with the Green Lakes area (Map 2A.25), another popular base of operations for climbing South Sister (a steeper route requiring the traverse of perennial snow fields not covered by this author). Views are marvelous from this vantage point, from Cayuse Crater on the southern flank of Broken Top to the east all the way around to Rock Mesa on the west (Figure 2A.47).
Figure 2A.47. The silicic Rock Mesa Flow and Little Broken Top lava dome from the neoglacial Little Ice Age moraine of the Lewis Glacier.
The trail then climbs in earnest, traversing a seemingly endless, steep slope of reddish, oxidized basaltic to andesitic scoriaceous cinders, and lava blocks and bombs that make up the summit cone of South Sister. Figure 2A.48 presents the view you’ll receive looking toward the southeast from the cirque headwall above the Lewis Glacier. The Little Ice Age terminal moraine is readily observed encircling the glacier’s terminus. In the middleground, one can see the aligned silicic domes and flows of the Devil’s Hill Volcanic Chain, while in the background the volcanoes of the Mount Bachelor Volcanic Chain march off in the distance. Once you reach the rim around South Sister’s ice-filled summit crater, in a tough three-quarters of a mile, walk to the right and make for the highest point on the summit, then continue circumnavigating the crater’s entire perimeter (Map 2A.25). It’s roughly eight-tenths of a mile around the rim, and the views are superlative in all directions. This is the prize you have likely anticipated and you will not be disappointed.
Figure 2A.48. A view from the cirque headwall above the Lewis Glacier looking southeast; Moraine Lake lies in the middle distance to the far right, while Mount Bachelor lies on the center skyline.
As you make your trek around these lofty heights, note that the volcano’s rim is comprised of scoria, lava bombs, and agglutinate spatter. Figure 2A.49 offers just one of any number of unusual scoriaceous volcanic bombs you might encounter. You’ll see a number of Oregon’s premier composite volcanoes on your traverse, beginning with Mount Bachelor to the southeast, a basaltic andesite stratovolcano erupted near the close of the Pleistocene. This volcano’s nearly perfect symmetry belays its youth. Contrast it with Broken Top Volcano lying further to the east, its flanks are considerably eroded by glacial activity which has exposed its feeder dike systems, lava flows, and near-vent volcanic breccias. Broken Top is a much older stratovolcano with an age and composition similar to that of North Sister. It is chiefly comprised of basaltic andesite, although it is built on a base of older rhyodacite and dacite similar to Middle and South Sister (Taylor, 1968 and 1981; Taylor et al., 1987). Still looking eastward, the Green Lakes occupy the glaciated valley between Broken Top and South Sister. Nearer yet, you can see the rough, gray rhyodacitic Newberry and Miller lava domes and their associated flows, major Holocene silicic eruptive centers on South Sister’s southern flank that formed as part of the Devil’s Hill Volcanic Chain. As you walk, Teardrop Pool, an annual summer-season meltwater pond formed within South Sister’s crater, shimmers to you right (Figure 2A.50).
Figure 2A.49. A volcanic bomb observed on South Sister’s summit; note the typical tear-drop shape, its denser, porphyritic, oxidized exterior, and its pumiceous interior.
Figure 2A.50. Teardrop Pool annually melts out of the perennial snowfield filling South Sister’s crater.
When you reach South Sister’s true summit, fine views unfold along the north side of the mountain (Figure 2A.51). To the northeast lies the Whychus Creek drainage basin, from Tam McArthur Rim and Broken Top to the east, to the glacially scoured east face of South Sister before you, to the Chambers Lakes area and on to Middle Sister, North Sister, and finally Black Crater in the north. At its maximum 24,000 to 18,000 years ago, the Suttle Lake ice mass covered this entire watershed (Figure 4B.2). The volcano’s summit offers a breaktaking view down onto Prouty Glacier. Looking down the axis of this glacier, notice Carver Lake, encircled by narrow, arcuate piles of loose debris, Little Ice Age terminal moraines of the Prouty Glacier.
Figure 2A.51. Your view to the northeast from South Sister’s lofty summit; North Sister lies in the middleground, with Mount Jefferson pushing skyward on the horizon just to the left of it.
South Sister’s two younger siblings make up much of the northern skyline. All three of these immense stratovolcanoes were built upon the older shield volcano material that initially filled the developing High Cascades graben beginning in the early Pleistocene. Comparing their state of symmetry, degree of erosion, and compositional differences, it is apparent that the three volcanoes decrease in age and become more intermediate southward (Taylor, 1968 and 1981; Taylor et al., 1987). North Sister is a basaltic andesite and andesite composite volcano constructed on a broad shield volcano base of basaltic andesite flows. Its flanks have been considerably eroded by glaciers and expose the central volcanic plug, dike systems, and near-vent volcanic breccias. Middle Sister is younger and South Sister is the youngest; both are composite volcanoes with much greater compositional variation and both lack a shield volcano base. Middle Sister is comprised chiefly of basalt porphyry lava flows and lesser amounts of basaltic andesite, andesite, dacite, and rhyodacite lavas and pyroclastic deposits. South Sister’s composition is more intermediate, mainly comprised of andesitic lava flows and a lesser amount of andesitic pyroclastics; although its southern flanks are blanketed in rhyodacite domes, lava flows, and tephra. Massive lava domes and flows of rhyodacite and dacite crop out around the lower flanks of each volcano, although South Sister more so than Middle Sister. Middle Sister’s silicic volcanism ended prior to late Pleistocene glaciation as all of its exposed silicic rocks show signs of the passage of ice. On the other hand, South Sister exhibits an abundance of Holocene silicic eruptive centers that exhibit the typical ragged, boulder surfaces of their youth.
Continue your counterclockwise circumnavigation, shortly you’ll reach a low point in the rim that provides access to a long narrow ridge on South Sister’s northwest slope and an alternate climber’s route (detailed in Field Trip 4B). Looking westward, the older, highly glaciated terrain of the volcanic platform comprised of basalt and basaltic andesite lavas and pyroclastic material originally built on the central High Cascades graben during the late Pliocene and early Pleistocene is prominently displayed (Taylor, 1968 and 1981; Taylor et al., 1987). This broad plateau is dissected by the headwater tributaries of the McKenzie and Willamette Rivers, and its gently westward-dipping slope is dimpled with resistant knobs such as The Husband and The Wife, the remnant summit cones and volcanic necks of eroded shield volcanoes and the source vents for the volcanism that formed this landscape. Ahead, Rock Mesa, the late Holocene silicic dome and lava flow complex observed yesterday from Little Broken Top, enters your field of view to the southwest. In the distance rises the Cascade Crest, looking somehow more subdued given its lack of impressive stratovolcanoes.
It is just a short distance to the junction with the climbing route you ascended earlier to complete your tour around South Sister’s summit crater. Now comes the easy part of your day; a quick four and a quarter mile descent back to your campsite. When you’ve rested, eaten dinner, and recovered from your day’s excursion, be sure to enjoy that sunset over South Sister from the shore of Moraine Lake (Figure 2A.52) as you reminisce over the events of the day.
Figure 2A.52. Sunset on South Sister from the shore of Moraine Lake; can you ever get enough of these?
If yesterday didn’t sap all your geology inquisitiveness, consider a day-hike to Le Conte Cone and the margin of the Rock Mesa Flow today. Once again, head southwest around the shore of Moraine Lake, and up the valley at its end to the trail junction at four-tenths of a mile (Map 2A.24). Instead of taking the climber’s route to the right, continue straight ahead on the trail toward the Devils Lake Trailhead. As you walk, notice the pumice lapilli, rock fragments of mixed lithology, and whitish silicic ash blanketing the surface; tephra from the Rock Mesa Eruption. At just over eight-tenths of a mile, you’ll cross a low ridge running northwest-southeast. Look back the way you came, to the north for a great view of South Sister Volcano and to the south of Devils Hill, an ice-sculpted, Pleistocene rhyolite dome. A four-way trail junction occurs at one mile; the Hell Creek Trail to Devils Lake Trailhead heads left (south), the main climber’s route to South Sister’s summit heads right (north). Continue straight westward (Map 2A.24); the trail soon passes through a low saddle and then begins a gradual, stepped descent to the Wickiup Plain. The trail curves gradually around Kaleetan Butte, a resistant, glaciated ridge of Pleistocene rhyodacite and dacite (Taylor et al., 1987). In about seven-tenths of a mile further, you should see the Rock Mesa Flow off to your right at 3:00, and in roughly one and a half miles from the last trail junction, you’ll reach yet another.
Turn right here and begin a diagonal southeast to northwest traverse of the Wickiup Plain (Map 2A.24). Almost immediately, a dark monolith of igneous rock juts out of the plain to your right in sharp contrast to the pumice strewn surface around it (Figure 2A.53). Take a moment to examine the jumbled columnar jointed basaltic rock exposed on its near side, indicative of the monolith’s nature, probably an old, much eroded, volcanic neck. As you continue walking, you’ll quickly notice the trail is heading directly toward a large conical hill with a notch in its near side, this is Le Conte Crater, a basaltic cinder cone erupted during the Holocene (its lava flow was observed at mile 130.8 on the Field Trip 2A road log) (Figure 2A.54). The notch actually occurs where the left flow levee of a major breach and gutter system merges with the southern flank of the scoria cone. The subdued nature of the cone and breach system is caused by the thick blanket of Rock Mesa tephra which covers everything in this area (its highly siliceous composition presents a poor environment for vegetation to become established, hence the Wickiup “Plain”). About six-tenths of a mile from your last trail junction, you’ll reach a low ridge, the tephra-blanketed lava flow issuing from Le Conte Crater’s breach. Head off-trail at this point, another four-tenths of a mile brings you to Le Conte Crater’s rim (Map 2A.24); and a quick four-tenths of a mile of additional hiking carries you completely around the crater and back to the point where you first reached its rim. The cinder cone’s northeastern rim offers excellent views of the Rock Mesa dome and flow (Figure 2A.55). Notice the coarse, blocky surface and steep flow margin attesting to the high viscosity of the extruded lava.
Figure 2A.53. A old volcanic neck protrudes from the edge of the Wickiup Plain.
Figure 2A.54. Le Conte Cone with South Sister Volcano and Rock Mesa lava dome and flow in the background.
Figure 2A.55. The view of the Rock Mesa silicic lava dome a flow from Le Conte Cone; South Sister lies in the middle ground to the left, while Broken Top lies in the background at center.
Descend Le Conte Crater, heading diagonally downward to your left to the base of the Rock Mesa Flow. This lava flow erupted about 2,000 years ago, and represents some of the most recent volcanic activity in the Cascade Lakes area. The grayish, fine-grained rhyodacite and glassy pumice and obsidian of which it is composed suggests a magma of relatively low temperature, but high water and silica content, the probable causes of its viscous nature (Figure 2A.56). Now follow the lava flow’s margin eastward to join an old, unmaintained trail and follow that upslope and onto an open plain blanketed in pumice fragments (Map 2A.24). You’ve come another mile. You can continue following the old trail right up onto the Rock Mesa Flow all the way to an observation point that looks out onto the Wickiup Plain. This author does not know the origin of this trail (its depicted on the South Sister USGS 7.5 minute quadrangle), but someone went to a great deal of trouble constructing it on the loose, craggy surface of the lava flow. It’s nearly two miles of additional work out and back from here, but walking across the viscous lavas are certainly interesting and the view down the Wickiup Plain is great. Eventually, you will need to head southeast along the western margin of the plain about half a mile to reconnect with the trail back to Moraine Lake (Map 2A.24). From there, its roughly one and seven-tenths of a mile back to your campsite.
Figure 2A.56. The margin of the Rock Mesa Flow; note the coarse, blocky surface, steep front, and abundance of glassy rubble, features attesting to the highly silicic, viscous nature of this volcanic material.
Take a break this afternoon; after that little trek, you deserve a rest or an afternoon swim in Moraine Lake; and don’t forget to take in a last sunset stroll.
Aaaah, sleep in today; you have only to hoist your pack and return to the Green Lakes Trailhead this morning, an easy reverse of the course you took in on your first day. Its all downhill, and by now, you know the way.
Mount Bachelor Trail (Tr 2A.3)
This hiking option is included mainly for completeness. Personally, this author doesn’t have many positive things to say about it. The views from the summit are nice enough and to the south they are different enough from the nearby South Sister and Tumalo Mountain summits to make them interesting, but the trail slugs upward for over three thousand feet, switchbacking beneath two chair lift routes all the way. Why take this trail then? Well, it sure beats paying for the ski lift ride from Egan Lodge on the northwest side of the mountain; a ride which dumps you off at Pine Marten Lodge only half way to the summit just so that you can “explore” the nearby muddy dirt roads and parking area, and then snap a quick picture in front of the weather-beaten lodge just like all the other tourists. If you’re willing to head off-trail, you can use this hike to access the well preserved latest Pleistocene and Holocene glacial record laid bare on Mount Bachelor’s northeast face; in fact, it is likely the most easily viewed record of neoglacial activity anywhere in the Oregon Cascade Range.
Parking in the informal parking area at the gated entrance to the Mt. Bachelor Ski Resort’s Sunrise Lodge and Chairlift is no longer permitted, so you’ll need to use the Dutchman Flat Snowpark instead (Map 2A.26). Park there, and walk about four-tenths of a mile east along the Cascade Lake Hwy to the gate. Pass around the gate and up the road on the left leading to the Sunrise Lodge parking area. Where the road begins to bend to the right cross the grassy median directly in front of you and walk straight southeast across the lower parking lot, through another grassy median, and across the upper parking lot to its back edge; in this way, the trailhead to the top of Mount Bachelor should be easily found. A small green sign marked “Trail” greets you at the start.
Almost immediately, the trail begins traversing an apron of bouldery outwash derived from end moraines perched higher on the northeast flank of Mount Bachelor. The outwash and moraines are believed to be associated with the latest Pleistocene Canyon Creek advance of the Cabot Creek glaciation (Scott, 1977). The first, subdued, bouldery ridge is reached in about three-quarters of a mile, probably the lowermost extent of the right lateral Canyon Creek moraines. The vegetation gradually becomes thinner and less robust and glimpses of the summit begin to come into view. At just over one mile, the trail crosses the access road to Pine Marten Lodge and in a couple hundred yards it climbs onto a more distinct ridge just east of a chair lift station midway to the summit (Map 2A.26). Note that the access road emerges from behind the right side of the building and continues diagonally upslope to the west. You will return to the trail via this road on your descent. Look westward above the access road. From your position, you can see a bouldery, tree-studded ridge just to the right of the chair lift paralleling the one you are on, and beyond that, the breached nose of a very fresh, sharp-crested ridge pokes above that one. The nearest ridge (the one you are on) is a right lateral moraine of Canyon Creek age, while the second and third ridges are late Holocene neoglacial moraines.
Continue climbing; initially, the trail ascends the Canyon Creek moraine ridge, but in about half a mile, the slope transitions from bouldery till to coarse, basaltic andesite tephra consisting of lava blocks and bombs. Immediately to your right lie the inner and outer right lateral neoglacial moraines; beyond lies the cirque carved into the northeast face of Mount Bachelor’s summit cone. In about three miles from the parking area, you eventually reach the summit area just right of the summit chair lift station (Map 2A.26). Now make your way to the actual mountain summit which lies upslope to the west; this direction takes you along the top of the cirque headwall sculpted into Mount Bachelor’s summit cone. Nice views of Broken Top and the Three Sisters open up to the northwest (Figure 2A.57). Egan Cone, composed of red scoria, sits on the lower slopes of Mt. Bachelor just beyond Pine Marten Lodge; volcanic eruptions associated with this cinder cone are the youngest in the Mount Bachelor volcanic chain. The lodge itself sits on a bench formed by the eruption of basaltic andesite lava flows from a major vent about midway up Mt. Bachelor’s northern flank.
Figure 2A.57. The Three Sisters (left) and Broken Top (right) viewed from Mt. Bachelor’s summit area.
Walk upslope and to the right along a service road around the northern rim of one of several summit craters marking the latest period of eruptions at Mount Bachelor. The entire summit area displays numerous vents and is composed of unglaciated basaltic andesite lava flows. Vents occur as low, blocky domes and as collapse craters. The summit vents and plugs exposed in the cirque headwall and on the summit cone are aligned in an elongate, northwest-trending ridge. Pyroclastic material is scarce, forming a few scoria cone remnants that are older than the summit domes and lava flows, indicating the latest eruptions were of a more fluid nature. In just under two-tenths of a mile, you reach a low point in the rim that provides an excellent view directly down the axis of the cirque (Figure 2A.58). The cirque was initially carved by a Canyon Creek glacier and later deepened by glacial erosion during two subsequent late Holocene neoglaciations that left nested terminal and right lateral moraines on the slopes north and east of the cirque (Scott, et al., 1989; Scott, 1990; and Scott and Gardner, 1990). The outer neoglacial moraine overlies and postdates Mazama Ash and contains tephra of Rock Mesa and Devil’s Hill scattered on its surface, while the inner moraine is not covered by the tephra of Rock Mesa and Devil’s Hill, suggests a later neoglacial advance, probably during the Little Ice Age.
Figure 2A.58. The northeast facing cirque carved into Mt. Bachelor’s summit cone, its lower end and east side encircled by fresh, sharp-crested neoglacial moraines; the Cascades Lake Highway can be seen in the middleground, with Broken Top (left) and Tumalo Mountain (right) beyond.
Views from the top of Mount Bachelor are the highlight of this excursion! To the north, the major glaciated volcanic complex formed of the Three Sisters and Broken Top stratovolcanoes dominates the view (Figure 2A.59). To the west and southwest, you can see the headwaters valley of the Deschutes River. Several of its lakes are visible, some dammed by lava flows, and others by late Pleistocene glacial moraines. The four northernmost lakes (Sparks, Elk, Hosmer, and Lava) have no surface outlets, but water drains out through permeable glacial deposits and post-glacial lava flows and emerges as springs along the down- valley lava-flow margins. Little Lava Lake (or Lava Lake during exceptional high-water years) is the origin of surface drainage for the Deschutes River. To the southwest, Diamond Peak, Mount Thielsen, and Mount Scott form prominent north to south peaks in the distance, although the bulk of the High Cascades is formed of lower, older shield volcanoes in that direction. To the south and slightly east, the smaller shield volcanoes and cinder cones of the Mount Bachelor volcanic chain are visible; while Newberry Volcano, dimpled with volcanic cones and domes, forms the massive shield-like edifice to the east.
Figure 2A.59. Sparks Lake lies at the northwest base of Mount Bachelor in the uppermost Deschutes watershed, the Three Sisters stratovolcanoes serving as a backdrop; note the prominent late Holocene silicic domes and lava flows perched on South Sister’s southern flank.
At this point, you may return the way you came, or head off-trail to complete a short loop around the west side of Mount Bachelor’s cirque; choosing the latter route requires some care as you maneuver over rough terrain back down slope to the access road to Pine Marten Lodge. Begin your descent from the left edge of the summit rim (Map 2A.26); work your way down the slope that forms the western headwall of the cirque past a prominent rocky knob. Soon, the rough, black basaltic andesite lava blocks and bombs of the summit cone give way to gray bouldery till of the neoglacial moraines on the cirque’s lower west side. Angle your way downward onto the inner neoglacial moraine for a good view back up into the cirque, then walk northwest over the outer neoglacial moraine crest and down its outer slope to join the access road to Pine Marten Lodge (Map 2A.26). Once on the road, head down hill to the right, crossing the open terrain just upslope from the chairlift station you passed midway into your ascent earlier in the day. When you reach the trail, turn left and continue downslope to the parking area at the entrance road to Sunrise Lodge.
Tumalo Mountain Trail (Tr 2A.4)
The hike to Tumalo Mountain’s summit is a fairly simple three and a half mile round-trip excursion suitable for families, and the scenic vista from the top is exemplar. The trail ascends the southwest flank of the mountain, climbing1200 feet in elevation, but it is an easy grade with plenty of switchbacks (Map 2A.26). The first half of the trail itself is fairly uneventful, however, from near its midway point, views to the south of Mount Bachelor and the other shield volcanoes of the Mount Bachelor volcanic chain begin to open up. This vantage point also provides a great view into the cirque on Mt. Bachelor’s upper northeast flank (Figure 2A.60). Near the summit, the trail traverses reddish cinders comprised of small lava bombs and scoria.
Figure 2A.60. The upper slopes of Tumalo Mountain afford a wonderful view southwestward of the Mt. Bachelor Volcanic Chain, including the main Mt. Bachelor, Kwolh Butte, and Sheridan Mountain summits north to south.
Eventually, you skirt the upper wall of Tumalo Mountain’s glacially sheared-off northeast face (Map 2A.26). This is a glacial cirque related to at least two periods of late middle and late Pleistocene glaciations that occurred in the Tumalo Creek watershed to the northeast (Figure 1E.1 and Figure 1E.2). At the summit of Tumalo Mountain, walk to the north, and your view northwest toward the Broken Top and South Sister stratovolcanoes is unprecedented (Figure 2A.61). Notice the degree of erosion of Broken Top relative to South Sister. South Sister was erupted between 90,000 50,000 years ago and has been affected only by the late Pleistocene Cabot Creek glaciation and one or more Holocene neoglacial events. Broken Top is a substantially older volcano, erupted as much as 300,000 years ago and subjected to more than one major glaciation (at least the Cabot Creek and preceding Jack Creek glaciations).
Figure 2A.61. The major glaciated volcanic complex formed of the Three Sisters and Broken Top stratovolcanoes dominates the northwest view from Tumalo Mountain’s summit.
Hiking Trail Maps
Map 2A.20. Color shaded-relief map of the southwest quarter of the Broken Top 7.5” Quadrangle showing segments of the Broken Top Loop Trail (Tr 2A.1) and Moraine Lake Trail (Tr 2A.2).
Map 2A.21. Color shaded-relief map of the northwest quarter of the Broken Top 7.5” Quadrangle showing segments of the Broken Top Loop Trail and Moraine Lake Trail (purple), as well as hiking routes to the Bend Glacier and the southern summit of Broken Top Volcano (orange).
Map 2A.22. Color shaded-relief map of the northeast quarter of the Broken Top 7.5” Quadrangle showing segments of the Broken Top Loop Trail and Tam McArthur Rim Trail (purple), as well as an alternate hiking route extending the Tam McArthur Rim Trail to an overlook of the Bend Glacier (orange).
Map 2A.23. Color shaded-relief map of the southeast quarter of the Broken Top 7.5” Quadrangle showing a segment of the Broken Top Loop Trail.
Map 2A.24. Color shaded-relief map of the southeast quarter of the South Sister 7.5” Quadrangle showing a segment of the Moraine Lake Trail (purple), as well as hiking routes to Le Conte Cone and Rock Mesa, Little Broken Top, and the summit of South Sister Volcano (orange).
Map 2A.25. Color shaded-relief map of the northeast quarter of the South Sister 7.5” Quadrangle showing a segment of the Moraine Lake Trail (purple), as well as hiking routes to Carver Lake and the summit of South Sister Volcano (orange).
Map 2A.26. Color shaded-relief map of portions of the Broken Top and Mount Bachelor 7.5” Quadrangles showing the Mount Bachelor Trail (Tr 2A.3) and the Tumalo Mountain Trail (Tr 2A.4).