Road Log

0.0 (0.0)       Refer to Map 1A.1.  Intersection of Franklin Avenue and U.S. Hwy 97 (3rd Street) in Bend, OR.  Drive south, remaining on Hwy 97 (3rd Street) through town.

0.3 (0.3)       Underpass beneath the Burlington Northern Santa Fe Railroad.  Road cuts on either side of the road expose typical basalts from Newberry Volcano’s lower flanks (Sherrod et al., 2004).  These basaltic lava flows have been offset by NW-SE trending faults along the Tumalo Fault Zone which extend through the Bend area (Jensen, 2006) and are highlighted in Field Trip 1C.

1.6 (1.3)       The highway passes over the Central Oregon Canal which diverts water from the Deschutes River for irrigation.

2.9 (1.3)       Hwy 97 (3rd Street) crosses a major northwest trending fault trace associated with the Tumalo Fault Zone.  The fault block to the northeast has been dropped downward.  Look carefully, another fault scarp of the Tumalo Fault Zone is clearly visible on Map 1A.1 north of Pilot Butte.

3.0 (0.1)       Junction of U.S. Hwy 97 (3rd Street) and the Bend Parkway.  Turn left (south) and remain on Hwy 97.

4.6 (0.9)       Refer to Map 1A.2.  Southbound off ramp to Baker Rd and Knott Rd, remain on Hwy 97.  Almost immediately, the highway crosses the Arnold Canal and another northwest trending fault trace here, with the northeast block dropped downward.

5.1 (0.5)       Northbound off ramp to Baker Rd and Knott Rd lies on the opposite side of the highway here.  Field Trip 1C diverges from the route here.

5.9 (0.8)       Good view of Lava Butte at 12:00; notice Lava Butte’s relatively small size and conical shape; geologist’s refer to this type of volcano as a cinder (or scoria) cone); U.S. Hwy 97 passes around the eastern side of this cinder cone.  This volcano and its associated lava flows form part of a northwest trending linament of cones and flows on Newberry Volcano’s lower northwest flank (Figure 1A.1).  They erupted along the Northwest Rift Zone (Jensen, 2006), a system of youthful normal faults that cut across Green Mountain northwest of Lava Butte and continues southeast to the East Lake Fissure above East Lake in Newberry Volcano’s caldera rim.

Figure 1A.1.  A simplified geologic map of the Northwest Rift Zone of Newberry Volcano showing the distribution of fissure vents, cinder cones, and basaltic lava flows (modified from Jensen, 2006).

9.4 (3.5)       Intermittent road cuts on both sides of the highway for about the next half mile reveal a thickening and then thinning blanket of dark tephra erupted from Lava Butte as the highway traverses across the NE trending axis of the cinder cone’s ash plume (Figure 1A.2).  Charcoal obtained from the base of the deposit indicates the tephra erupted about 7,000 years ago (Jensen, 2006).  A well-preserved section of Mazama ash occurs beneath the Lava Butte tephra.  Several cylindrical columns of reworked Lava Butte tephra were excavated here into the top of the Mazama ash during highway expansion in 1988 and Jensen (2006) indicates that these features represent the molds of trees rooted in the underlying Mazama ash.  The tephra buried the trees deeply enough to kill them, and as they subsequently rotted, volcanic cinders from the surrounding tephra filled the void to form the tree molds.

Figure 1A.2.  A simplified geologic map showing the successive lava flows from Lava Butte, the Gas-Line flows, tephra plumes associated with the lava flow-producing eruptions, and locations where the lava flows blocked and altered the course of the ancestral Deschutes River (tephra data from Jensen, 2006).

9.8 (0.4)       FS Rd 9710 lies on the opposite side of the highway here.  Field Trip 1B merges with the route at this point.

10.0 (0.2)     The basaltic aa lava flow margin from Lava Butte lies on the right side of the highway (Figure 1A.2); Lava Butte is in the background.  The highway continues around the eastern margin of the flow for about the next mile.

10.4 (0.4)     The Northwest Rift Zone of Newberry Volcano is expressed by a shallow fault scarp to the left side of the road here.

10.5 (0.1)     Gas-Line lava flows occur to the left and Lava Butte flows are to the right (Figure 1A.2).  The Gas-Line flows are also dated at about 7,000 years, but underlie the Lava Butte flows.  Jensen (2006) suggests eruptive activity along this portion of the Northwest Rift Zone began with vents near the Gas-Line flows and finally coalesced at a vent now under Lava Butte.

10.9 (0.4)     Junction of U.S. Highway 97 and FS Rd 9702.  Turn right (west) onto FS Rd 9702 and make an immediate right hand turn again into the entrance for the Lava Lands Visitor Center of Newberry Volcanic National Monument.  This part of the monument highlights Lava Butte (Figure 1A.3), a classically shaped Holocene cinder cone and its associated lava flows.

Figure 1A.3.  Lava Butte, a beautifully preserved, nearly symmetrical cinder cone that erupted about 7,000 years ago along the Northwest Rift Zone south of Bend, OR.

11.0 (0.1)     Continue through the entrance station (after paying the entrance fee) and make an immediate right turn onto FS Rd 9702-100, the road to Lava Butte’s summit.  Access to the summit is usually limited during the peak summer season to about 30 minutes per vehicle due to restricted parking; for a more leisurely and peaceful time, try to visit in the spring or fall.

Upon your return from Lava Butte’s summit, be sure to drive into Lava Land’s Visitor Center parking area via FS Rd 9702-100.  It is well worth your time to stop in and view the interpretive displays on geology, pre-history, Native Americans, and post-European arrival history.  If you have questions, talk to the on-duty park rangers.  Do not miss hiking the Trail of the Molten Land, accessed from behind the visitor center (see the Trail of the Molten Land, under Optional Hiking Trails at the end of this road log for a complete description of this hike).  This short, paved trail crosses the aa lava flow from Lava Butte and its gutter system, and climbs to a scenic viewpoint overlooking one of the subsidiary gutter channels, the Lava Butte flows, and the High Cascades volcanoes to the west.

11.2 (0.2)     Pass through the gate on FS Rd 9702-100 at the end of the parking area.  (This gate is normally closed from dusk to dawn and when the visitor center is closed.)  The eastern margin of Lava Butte’s aa lava flow is on the left (Figure 1A.2).

11.5 (0.3)     An old road cut in the edge of the flow exposes its internal structure; the rough, loose, blocky upper flow and the more-consolidated interior of the flow.  This structure is typical of basaltic aa flows; the upper flow cools and congeals more quickly than its interior and is broken up while the hot, plastic center still moves forward.

12.5 (1.0)     The view to the right from this location overlooks the breach and gutter system on Lava Butte’s southern flank from which the Lava Butte flows were extruded; stop for a quick peek if the road is free of traffic.

12.7 (0.2)     Parking area at the summit of Lava Butte.  Park here and walk up the stairs to the lookout tower and/or take a stroll around Lava Butte’s summit crater rim on the interpretive loop trail; scenic vistas abound wherever you choose to explore.  On a clear day from the summit area, a 360° panoramic view unfolds, exposing a plethora of central Oregon’s finest volcanically-generated topographic features.  The Cascade Crest from Mt. Jefferson in the north to Mt Bachelor in the south lies to the west of Lava Butte (Figure 1A.4) and Newberry Volcano’s shield-like profile, its northwestern flank lumpy with parasitic cinder cones, lies to the southeast (Figure 1A.5).

Figure 1A.4.  View from Lava Butte’s summit looking west toward Mt. Bachelor (left), Tumalo Mountain (center) and the Broken Top and Three Sisters Volcanoes (right); Lava Butte’s basaltic aa flows lay in the foreground.

Figure 1A.5.  Lava Butte’s summit crater with Newberry Volcano’s dimpled shield rising in the background.

Consider Lava Butte and its surrounding lava flows.  The Lava Butte and Gas-Line volcanic eruptions began about 7,000 years ago, producing small spatter cones and the Lava Butte cinder cone, a localized tephra sheet downwind of the eruptive center, and substantial basaltic aa lava flows covering roughly 9 square miles.  These eruptions were part of much more extensive volcanic activity associated with the Northwest Rift Zone (Figure 1A.1) that acted as a zone of weakness along which multiple vents began extruding magma at about the same time.  Greenwood Butte, lying northwest of Lava Butte, exhibits evidence of normal faulting associated with this rift zone (Figure 1A.6).  Other significant flows associated with the nearly 20-mile-long zone of volcanism are the Lava Cast Forest Flow and Mokst Butte Flow visited on Field Trip 1B.  Lava flows from Lava Butte oozed downslope toward the ancestral Deschutes River.  They successively filled portions of the valley and eventually blocked the stream channel in several locations, causing the formation of temporary lakes upstream of the lava dams (Figure 1A.2).  The Deschutes River was subsequently diverted into its present channel, producing a series of waterfalls where resistant bedrock remains.

Figure 1A.6.  Greenwood Butte lies northwest of Lava Butte and is bisected by normal faulting related to development of the Northwest Rift Zone.

Initially, in the immediate area, highly gas-charged and fluid magma began moving upward through several fractures within the Northwest Rift Zone, erupting along a 1.5-km-long fissure zone, probably in fire fountains much like those witnessed in Hawaii.  Much of the evidence for these short- lived eruptions is now buried under the subsequent volcanic products of Lava Butte, but some of the small spatter cones and pahoehoe flows generated along the fissure can still be seen as the Gas-Line flows across Hwy 97 from the visitor’s center.  Eventually, most of the fissure was sealed off by accumulating lavas and volcanic activity became concentrated at a major vent underlying Lava Butte.  As the magma became less fluid, frothy lava fragments accumulated as cinders around the vent in a conical-shaped mound that eventually formed the Lava Butte cinder cone we see today.

Occasionally, particularly powerful eruptive episodes must have sprayed finer cinders downwind to blanket the landscape as the tephra plume concentrated northeast of Lava Butte.  A southwesterly wind must have prevailed during much of Lava Butte’s formative period as evidenced by the asymmetric distribution of the tephra plume and the cinder cone’s larger volume of cinders and higher rim on its northeast flank.

Subsequently, as the gaseous magma was depleted and replaced by a denser, more viscous fluid, the weaker southern flank of the cinder cone was breached.  Lava poured out of the cone’s side and down slope to form several overlapping flows, mainly to the northwest of Lava Butte.  The earlier, more substantial flows were fluid enough to spread over five miles to the west and north, filling the valley of the ancestral Deschutes River and blocking its channel in several places (Figure 1A.2).  Later flows were more viscous and less voluminous, stacking upon each other closer to the vent, and sometimes forcing  new pathways around previous obstructions to cover new ground.  Over a relatively short period of time, probably only several years, lava flows spread over an area covering more than 9 square miles (Figure 1A.2), while Lava Butte reached a height of over 500 feet above the surrounding topography.

Where the Lava Butte flows blocked the channel of the ancestral Deschutes River, the stream was forced to find a new course (Figure 1A.2).   During the initial period of blockage, the valley of the ancestral Deschutes River was flooded upstream of the lava obstructions, forming several temporary lakes.  These lakes have long since vanished and appear as broad meadows today, filled with sediment carried in by the river or washed from the surrounding hills, and/or drained as a consequence of the river downcutting and the forming of a new stream channel.  Lava Island Falls, Dillon Falls, and Benham Falls occur in their present locations because the Deschutes River is still incising through resistant bedrock, either remnants of the Lava Butte flows themselves, or older volcanic rock through which the river was rerouted.  Many of these features of the Deschutes River’s recent evolution will be explored in detail, later on this field trip.

Return to your vehicle when you have absorbed as much as you desire, and drive back the way you came.

14.6 (1.9)     Back to the junction of FS Rd 9702 and U.S. Hwy 97.  Turn right (south) onto Hwy 97.  The highway drops steadily from the ridge-forming lava flows of the Northwest Rift Zone over the next several miles.

15.6 (1.0)     The highway passes over Lava River Cave near here.  Not to worry though, the lava tube’s roof is at least 50 feet thick.

15.7 (0.1)     Road cuts for about the next three-tenths of a mile expose the basalts of the Lava River Cave Flow, believed to be the equivalent of the middle to late Pleistocene Basalt of Bend.  The vent for this extensive flow occurred upslope from here, but is now buried by younger lavas.

17.1 (1.3)     Refer to Map 1A.3.  The highway passes over younger basaltic lava flows here, erupted from a chain of cinder cones to the left (east), the largest of which occurs at the site of the Camp Abbot cinder pit visited on Field Trip 1B.

17.8 (0.7)     Refer to Map 1A.4.  Sunriver Junction highway interchange.  Take Exit153 which provides access to FS Rd 9720 and a continuation of Field Trip 1B on the left (east), or FS Rd 40 and a divergence to Field Trip 1A to the right (west).

18.2 (0.4)     Junction of Hwy 97 off-ramp and FS Rd 40.  Turn right (west) onto FS Rd 40 toward Sunriver, OR to remain on Field Trip 1A.

19.5 (1.3)     Three-way intersection here.  Be sure you remain on FS Rd 40 (the leftmost road).

20.7 (1.2)     The road passes over the Deschutes River at this location.  Notice the flatness of the valley floor in this area, especially the open meadows to the right (north).  When the Deschutes River was dammed by the Lava Butte Flow, water backed up in the valley above the lava dam to form Lake Benham (Figure 1A.7).

Figure 1A.7.  Map outlining the initial maximum, and subsequently more stable, extent of  Lake Benham and its association with the lava flows of the Northwest Rift Zone (modified from Jensen, 2006).

The dam developed where the lava flow pouring in from the east lapped up onto an existing ridge formed by a 1.8 million year old rhyolite dome on the western margin of the valley.  The lake eventually filled to the elevation of a low point in the ridge (the lava flow from Lava Butte was at a higher elevation than this saddle), and lake water began spilling through the notch. At its maximum depth, Lake Benham would have filled an area of the valley floor to an elevation about equal to 4180 feet, some 20 feet above the FS Rd 40 bridge across the Deschutes River.  This lake level was likely temporary, however, because water pouring through the ridge gap would have rapidly incised into its soil and weathered bedrock cover.  Once the new river channel had begun carving into much more resistant, “fresh” bedrock at a depth of about 20 feet, Lake Benham stabilized at an elevation of about 4160 feet (about level with the FS Rd 40 bridge) for a much longer period, perhaps several millennia.  This smaller, shallower version of Lake Benham probably covered about 5 square miles and extended about 19 miles upvalley.  Where FS Rd 40 crosses the valley, the lake at its maximum level was about 2.0 miles wide, while the lake at its stabilized level was about 0.4 miles wide.  The valley is filled with as much as 2.5 meters of diatomaceous sediment, especially along its deepest, axial portion, which immediately overlies soil developed in Mazama ash from Crater Lake.  This sediment, dated between 6,700 and 1,900 years old, accumulated on the floor of the lake prior to its disappearance, and resulted in the flat valley floor observed today.

22.4 (1.7)     Junction of FS Rd 40 and FS Rd 41.  Turn right (north) onto FS Rd 41.

28.2 (5.8)     Refer to Map 1A.3.  Look to your right here; intermittent openings in the forest offer views of the Lava Butte Flow and the Deschutes River. Grassy meadows occupy former small lake basins formed as the Lava Butte Flow temporarily dammed the Deschutes River in several places.

29.7 (1.5)     Junction of FS Rd 41 and FS Rd 41-400, the entrance road to Benham Falls Overlook and the Slough Day Use Area.  Turn right (east) onto FS Rd 41-400.

30.6 (0.9)     Entrance road to Slough Day Use area on the left.  Continue on FS Rd 41-400.

31.9 (1.3)     Parking area for the Benham Falls Overlook.  Park here and walk the short distance to one or more scenic viewpoints of Benham Falls (Figure 1A.8).

Figure 1A.8.  Benham Falls, formed where lava from Lava Butte blocked the course of the Deschutes River, forcing the channel to incise through the older volcanic rocks of Benham Dome.

This is a good location to consider in greater detail the influence that the Lava Butte Flow had on the evolution of the Deschutes River and its channel morphology in this area.  As a general rule, streams seek a path of least resistance.  The ancestral Deschutes River was no different.  The old valley’s shape and position was strongly influenced by the natural topographic low formed between lava flows pouring in from Newberry Volcano’s flanks to the east, and older Cascade Range volcanic rocks to the west.  In a sense, the Newberry flows had forced the older river to the west, up against the Cascade Range rocks.  Figure 1A.2 shows the position of the Deschutes River prior to eruption of the Lava Butte Flow (roughly before 7,000 years ago); its position reconstructed from topographic evidence and borehole data (Jensen, 2006).  Notice that the former stream channel flowed completely around the ridge formed of an old, resistant rhyolite dome (Benham Dome), instead of across it (where Benham Falls exists today),and down through a natural topographic low that occurred approximately at the boundary between Newberry volcanic rocks on the east and Cascade Range volcanic rocks on the west.

About 7,000 years ago, the earliest and largest of Lava Butte’s flows flooded portions of the Deschutes River valley from the east, filling the ancestral stream channel to depths of more than 100 feet in some places, and obliterating much of the former stream’s course from near the Benham Falls Day Use Area, downstream to the Lava Island Falls Day Use Area (Figure 1A.2).  Water was ponded behind several lava dams to form temporary lakes upstream of the obstructions, such as Benham Lake (Figure 1A.7). Naturally, these lakes filled to a height where they could overtop the newly created lava dams, and then water gushed over the first convenient low spot in the dam, eroding a new stream channel in the process.  At the modern sites of Lava Island Falls and Dillon Falls to be visited later on this field trip, the Lava Butte Flow formed the dam which was overtopped.  Uniquely, however, at Benham Falls, the dam developed in two parts where the lava flow pouring in from the east lapped up onto the pre-existing ridge formed by a 1.8 million year old rhyolite dome (Benham Dome) on the western margin of the valley (Figure 1A.2).  The lake (Benham Lake) eventually filled to the elevation of a low saddle in the rhyolite ridge, a notch that happened to be lower than any point along the lava flow from Lava Butte, and lake water began spilling through the saddle.  The river rapidly downcut through the less resistant soil and weathered bedrock that covered the ridge comprising Benham Dome, but eventually encountered much more resistant unweathered volcanic rock at depth.  Benham Falls is today located at the position where the Deschutes River is still actively tearing away at this resistant material.

In all likelihood, there were initially many more such dams and associated waterfalls, however, over time these have been removed by erosion.  Today, the flat meadow bottoms sandwiched between the Lava Butte Flow on the east and the former western margin of the ancestral Deschutes River valley on the west, and located above Lava Island Falls, Dillon Falls, and Benham Falls, attest to the existence of temporary lakes that formed upstream of these channel obstructions (Figure 1A.2 and Figure 1A.7).  These lakes disappeared through drainage and filling, as the river incised its channel through the barriers and as sediment was washed in by the river and from the older volcanic terrain to the west.  The largest and presumably longest lasting of these lakes was Lake Benham, formed where the broad meadows occur in the shallow Deschutes River valley above the Benham Falls channel obstruction, as discussed earlier.

34.1 (2.2)     Return via FS Rd 41-400 to the junction with FS Rd 41.  Turn right (north) onto FS Rd 41.

35.0 (0.9)     A large road cut on the left side of the road here exposes Bend Pumice, one of several significant air-fall pumice and ash-flow tuff deposits erupted from the silicic Tumalo volcanic center east of Broken Top (Taylor, 1978; Hill and Taylor, 1989; and Hill and Scott, 1990).

35.4 (0.4)     The road crosses a NW-SE trending fault trace, marked at this location by the small draw.  Displacement is down to the southwest.

35.5 (0.1)     Junction of FS Rd 41 and FS Rd 41-600, the entrance road to Dillon Falls Day Use Area.  Turn right onto FS Rd 41-600.

36.2 (0.7)     “Y” fork in FS Rd 41-600.  The road to the left leads to a boat takeout site, continue right on the main road which leads immediately to the day use area.

Use the trailhead parking area for the Dillon Falls Day Use Area.  Hike downstream, past the boat takeout, to several excellent views of Dillon Falls.  As you walk along the river, look upstream into Ryan Meadow, this meadow is likely the site of a former lake that resulted from downstream blockage of the Deschutes River channel by the Lava Butte Flow.  Dillon Falls occurs where the modern Deschutes River merges back into its ancestral channel.  The falls tumble over lava still partially plugging the old river channel in a series of steep rapids (Figure 1A.9).  The nearness to the falls, the noise, and the rush of the crystal-clear water is really quite spectacular.

Figure 1A.9.  Dillion Falls forms where lava flows from Lava Butte still plug the Deschutes River channel.

37.1 (0.8)     Return via FS Rd 41-600 to the junction with FS Rd 41.  Turn right (north) onto FS Rd 41.

37.9 (0.8)     The road crosses a major NW-SE trending fault, related to the Tumalo Fault Zone, with displacement down to the northeast.  The fault scarp forms a prominent bluff on the west bank of the Deschutes River downstream of Dillon Falls (Map 1A.3).

42.3 (4.4)     Junction of FS Rd 41 and FS Rd 41-800, the entrance road to Lava Island Falls Day Use Area.  Turn right onto FS Rd 41-800.

42.9 (0.6)     FS Rd 41-870 on the left leads to the Lava Island Rock rafting takeout area.  Remain on FS Rd 41-800.

43.0 (0.1)     Parking area for the Lava Island Falls Day Use Area.  Park here and follow the trail downstream, past the rafting takeout area to an overlook of Lava Island and Lava Island Falls.

The Lava Butte Flow filled the channel of the ancestral Deschutes River here to a depth of approximately 100 feet, extending downstream in a narrow ribbon confined to the old canyon for nearly a mile.  The river eventually carved two channels through the lava dam to either side of the resistant lavas filling the old canyon.  An intake for an irrigation canal was installed on the east bank of the river just above Lava Island Falls.  The raised bed of the canal, built on wooden trestles, can be viewed across the river from the main overlook, snaking its way downstream along the canyon wall.

43.7 (0.7)     Return via FS Rd 41-800 to the junction with FS Rd 41.  Turn right (north) onto FS Rd 41.

44.1 (0.4)     Intersection of FS Rd 41 and FS Rd 46 (Cascade Lakes Highway).  Turn right (northeast) onto FS Rd 46 toward Bend, OR.  Field Trip 1A merges with Field Trip 3A here.

45.7 (1.6)     Refer to Map 1A.5.  The highway crosses the trace of a NW-SE trending fault here, withdisplacement down to the northeast.

46.8 (1.1)     Refer to Map 1A.1.  The highway crosses yet another NW-SE trending fault trace at this location related to the Tumalo Fault Zone, with displacement down to the northeast.

Just ahead, the road descends through a narrow, dry valley; observe the ridges on either side of the road.  These features are classic examples of the geologic process known as topographic inversion (Jensen, 2006).  Figure 1A.10 explains the process.  In this area, silicic pyroclastic rock units erupted from the Tumalo volcanic center (Taylor, 1978; Hill and Taylor, 1989; and Hill and Scott, 1990) were laid down in uniform layers to form a rolling tableland.  Streams flowing from the topographic highlands to the west cut valleys into these pyroclastic rocks.  Subsequent lava flows from the High Cascades then poured down these valleys from the west, destroyed the drainage systems, and formed elongated bodies of resistant basaltic rock.  Later, the tributary streams of the older, now buried drainages still entering from the sides incise new channels into the less resistant pyroclastics along the margins of the elongate lava flows.  As these younger streams cut their own valleys, the lava flows which once occupied the topographic lows within the older drainages are now preserved as basalt-capped ridges between modern stream valleys.

Figure 1A.10.  A diagram displaying the process of topographic inversion; differential erosion preserves the more resistant lavas, eventually leaving them standing above the less resistant pyroclastic deposits.

47.9 (1.1)     Bend city limits.  FS Rd 46 (Cascade Lakes Highway) becomes South Century Drive.

48.8 (0.9)     Intersection of South Century Drive, Mt. Washington Drive (on the left), and SW Reed Market Rd. (on the right).  Continue north through the round-about on South Century Drive.

49.0 (0.2)     Intersection of South Century Drive, SW Chandler Avenue (on the left), and SW Colorado Avenue (on the right).  Continue north through the round-about on South Century Drive.

49.5 (0.5)     Intersection of South Century Drive and Simpson Avenue.  Continue north (straight) through the round-about on South Century Drive.  South Century Drive becomes NW 14th Street here.

50.1(0.6)     Intersection of NW 14th Street and NW Galveston Avenue.  Turn right (east) onto NW Galveston Avenue.

50.4 (0.3)     Cross the Deschutes River.  NW Galveston Avenue becomes NW Tumalo Avenue after crossing the river here.

50.5 (0.1)     Junction of NW Tumalo Avenue and NW Riverside Boulevard.  Turn left (north) onto NW Riverside Boulevard.  NW Riverside Boulevard curves gently to the east along the river and passes into downtown Bend.

51.0 (0.5)     Traffic light. Intersection of NW Riverside Boulevard and NW Wall Street.  Continue east through this and one more traffic light; NW Riverside Boulevard becomes Franklin Avenue after the first light.

51.4 (0.4)     Overpass for the Burlington Northern – Santa Fe Railroad.  Road cuts on either side of Franklin Avenue are in the Basalt of Bend (Sherrod et al., 2004).

51.6 (0.2)     Intersection of Franklin Avenue and Oregon Highway 97 (3rd Street).  This ends Field Trip 1A.

Road Route Maps

Map 1A.1.  Color shaded-relief map of the Bend 7.5” Quadrangle containing segments of Field Trip 1A-F and Field Trip 2.

Map 1A.2.  Color shaded-relief map of the Lava Butte 7.5” Quadrangle containing segments of Field Trip 1A, 1B, and 1C, as well as Field Trip 2A.

Map 1A.3.  Color shaded-relief map of the Benham Falls 7.5” Quadrangle containing segments of Field Trip 1A, 1B, and Field Trip 2A.

Map 1A.4.  Color shaded-relief map of the Anns Butte 7.5” Quadrangle containing segments of Field Trip 1A and 1B,  Field Trip 2A, and Field Trip 3A.

Map 1A.5.  Color shaded-relief map of the Shevlin Park 7.5” Quadrangle containing segments of Field Trip 1A, 1D, and 1E, as well as Field Trip 2A.

Optional Hiking Trail

Trail of the Molten Land

This is a short, easy hike on a paved trail with several interpretive signs; it is designed to be family-friendly and much of it is handicap accessible.  The trail traverses one of the youngest lava flows from Lava Butte (Figure 1A.2 and Figure 1A.3).   You can stroll through a well-preserved breach and gutter system on the cinder cone’s southern flank, the source of Lava Butte’s flows and observe many classic lava flow features along the way.

Begin at the trailhead sign for the Trail of the Molten Land which starts on the paved trail that circles behind the Lava Lands Visitor Center and quickly climbs onto the margin of the aa lava flow associated with Lava Butte’s third eruptive episode (Figure 1A.2 and Map 1A.1.1).  Notice the angular, blocky nature of the lava flow surface, a characteristic feature of basaltic aa lava.  The aa lavas here formed when the normally low silica content of basaltic magma is slightly greater than average, high enough to increase the extruded lava’s viscosity and reduce its ability to flow.  Water content, low in basaltic lava to begin with, was also likely lower than average.  The surface of the flow cools and solidifies, breaking up into jagged chunks as the still hot, taffy-like lava continues to flow slowly beneath.

A “Y” junction in the trail occurs at about 0.17 miles.  Take the right fork which soon passes several massive, rounded “armored lava balls” near 0.21 miles (Figure 1A.1.1).  Try to imagine large chunks of still hot, semi-solid lava breaking loose from the flow and being rafted along at the surface.  As these blocks were rolled and tumbled within the flow, they accumulated mass as more lava and solidified blocks were plastered to their exteriors in irregular layers. A right-hand bend in the trail occurs at 0.24 miles; the main lava channel exiting Lava Butte’s breach lies to your left.  At 0.32 miles, you are standing on the east levee of the lava gutter which formed in the breach on the southern flank of Lava Butte associated with the third eruptive stage; its main channel lies upslope and to the left.  The trail descends into the lava gutter, and you can see multiple levees or “bathtub rings” plastering the east side of the gutter channel at progressively lower levels.  These features represent the gradual decrease in magma volume during the vent’s final eruptive episode.

Figure 1A.1.1.  Massive, rounded, “armored lava balls” perched on the surface of the youngest Lava Butte flow.

At 0.37 miles, follow the short spur trail to the Phil Brogan Overlook at your right.  A small lava tube can be observed near the trail at 0.41 miles associated with Lava Butte’s final eruptive period.  This tube formed as the final pulse of lava poured through the gutter.  Lava tubes form as the flow surface cools and solidifies, encasing and insulating the flow’s interior.  Still fluid lava within moves down slope and the tube is evacuated.  Above this location, you can see straight into the cinder cone’s breach (Figure 1A.1.2).  Behind you, an older lava channel is dammed on the right-hand side of the main channel you are standing in.  At 0.46 miles, the main channel shows further evidence of bifurcation, with the older channel on the left plugged by lava and a younger channel to the right following the same path as the lava tube you just passed.  As you climb the spur trail, examine the west side of the gutter channel.  Multiple layers of lava are stacked on the levee here, each representing a separate eruptive pulse.  At about 0.50 miles, the trail crosses the western levee of the main channel of the breach’s gutter system and begins traversing along the southern edge of a side channel associated with Lava Butte’s fourth eruptive stage (Figure 1A.2).  As you can see, when eruptions progress, channel obstructions form that often divide into multiple distributary pathways downstream within lava flows.  The head of this subsidiary branch of the gutter system is plugged by the levee formed during the main channel’s final eruptive episode.  Look across the gutter to the side channel’s high northern wall and note the polygonal pattern (Figure 1A.1.3).  These are columnar joints formed perpendicular to the lava’s surface; this indicates that lava was plastered to the wall here, probably each time the gutter channel was occupied by a fresh outpouring of lava.

Figure 1A.1.2.  Lava gutter formed at the breach on the southern flank of Lava Butte cinder cone.  This is the source of the Lava Butte Flow.

Figure 1A.1.3.  Columnar joints, normally formed perpendicular to the lava’s cooling surface; their orientation here indicates that lava was plastered to the wall of the lava gutter, probably each time the gutter channel was occupied by a fresh outpouring of lava from the breach upslope.

You reach the Phil Brogan Overlook at 0.52 miles from the trailhead.  This location offers an impressive view of the High Cascades stratovolcanoes from the tip of Mt. Jefferson in the north to Mt. Scott (on Crater Lake’s caldera rim) in the south.  Observe the direction that lava flowed as it issued from the side channel below you during the fourth eruptive episode.  It poured out to the southwest, but curved around to the west as it flowed down slope toward the Deschutes River.  Turn around and return to the main trail.

Rejoin the main trail at 0.68 miles and continue walking around the loop to your right.  The trail passes a nice example of a cooling fracture in the lava flow surface on your right at 0.76 miles.  Cooling fractures are a common feature observed on youthful lava flows, formed when the hot, inflated flow was cooling, contracting, and losing volume.  At 0.80 miles, the trail passes along side several prominent lava “squeeze-ups”.  These features are formed where still molten or hot, taffy-like lava squeezes upwards through cracks formed in the cooler, more rigid and brittle crust of the lava flow.  In a few hundred feet, several more “armored lava balls” can be observed half buried in the aa lavas near the trail.  The trail loop closes at 0.86 miles; continue right toward the edge of the lava flow and the visitor center and reach trail’s end at 1.04 miles.

Hiking Trail Map

Map 1A.1.1.  Color shaded-relief map of a portion of the Lava Butte 7.5” Quadrangle showing the Trail of the Molten Land (Tr 1A.1) at the Lavalands Visitor Center of Newberry Volcanic National Monument.