Newberry volcano is located E of the Cascades.  It is a massive shield-shaped composite volcano, 2,434 m at its highest point, covering over 1,600 km2.  The primary shield was constructed by basalts and basaltic andesites.  It has over 400 cinder cones on it.  The volcano produced major silicic eruptions forming a 6 x 8 km caldera at its summit.  The caldera contains two lakes, a post-caldera cinder cone, and the Big Obsidian lava flow, the most recent activity of the system.  There are hot springs and a single fumarole present.  It is considered to be an active volcano.

Newberry is the largest volcano in footprint and volume in the Cascades, though as a shield, it certainly isn’t the tallest.  There is a discrepancy between its reported footprint.  Smithsonian GVP carries an area of 1,600 km2 while the USFS carries it as 3,100 km2. 

The caldera is located some 60 km S of Bend and 31 km E from La Pine.  It is the largest developed area within the surrounding National Monument.  The caldera has medium use most of the year, with high use during peak times.  The National Monument averages 250,000 visitors yearly.  There are 12 multiuse trails within the caldera, boat launches at the lake, and nine campgrounds.  Winter activities include snowmobiling, snowshoeing, and cross-country skiing.  Ice fishing wouldn’t surprise me, though it is not mentioned.  Local hotels and resorts offer rooms for rent.  The two crater lakes are popular for water recreation and are stocked for fishing. 

16,000 live within 30 km and 180,000 within 100 km.  The closest cities to Newberry are Bend (103,000), 37 km N and La Pine (2,500), 24 km W.  US 92 is the major N-S highway connecting the two cities to the W.  There are a cluster of smaller towns along the highway between the two cities.  Tourism is the major economic driver in this part of Oregon with multiple ski areas, hiking, biking, rafting, camping, fishing, rock climbing, and related outdoor activities available.  In recent years, it has become a commuter town for tech workers from Silicon Valley and a retirement community. 

The system is located to the W of the crest of the Cascades Volcanic Arc in its rain shadow.  The climate is classified as semi-arid (high desert).  Annual precipitation is 28 cm, with 60 cm of snow.  Temperature ranges in this part of Oregon are 16° – 1°C, with record high of 42° C and record low of -32° C.  This makes for a rather short growing season with freezing temperatures on average found mid-Sept – mid-Jun. 

The 222 km2 Newberry National Volcanic Monument was created within the larger Deschutes National Forest in 1990.  It includes the summit caldera, parts of its upper slopes and most of the NW Rift Zone.  Primary visitor destinations are Lava Butte, Lava River Cave, Lava Cast Forest, and Newberry Caldera.  There are multiple visitor centers.  Lava River Cave is open to visitors throughout the summer and is the largest uncollapsed lava tube in Oregon.  Lava Cast Forest was created by a 6 ka lava flow that created molds of trees at the time of its eruption.  Lava Butte is a cinder cone some 18 km S of Bend. 

Volcano observation and monitoring in this part of Oregon is done by the Cascades Volcano Observatory located in Vancouver, WA.  There are at least 11 active seismometers and GPS transmitters dedicated to Newberry. 

Region

We most recently visited this part of the Cascades volcanic arc and central Oregon with our two part Jun 2025 and Jul 2025 Belknap post.  Belknap itself is some 80 km NW from Newberry.  The Three Sisters / Brokentop / Mount Batchelor volcanic complex are even closer, with Mount Batchelor 46 km NW from Newberry.  With that in mind, this post will take a short look at regional volcanoes E, W and S of Newberry.  Readers interested in volcanoes to the N and NW should take a look at the extende Belknap posts. 

Newberry is an interesting location, some 60 km E of the Cascade volcanic arc.  Volcano Discovery lists at least 16 volcanic centers along the 120 km part of that arc between Mount Batchelor 46 km NW of Newberry and Mount Mazama (Crater Lake), 111 km SE from Newberry.  Mount Shasta is much farther SSW, nearly 270 km.  We will confine our discussion of regional volcanism to the two most recently active volcanoes to the W of Newberry along the main Cascades arc and the 6 volcanic systems SE and S of Newberry itself.  All distances are measured from the location of Newberry listed by the Smithsonian GVP Newberry entry.

Davis Lake

The Davis Lake volcanic field is located 50 km WSW from Newberry.  It has three andesitic Holocene cinder cones and associated young looking lava flows.  The cinder cones and flows are aligned N-S at the base of a group of young basaltic andesitic shields.  The northernmost lava flow dammed local drainage creating Davis Lake at the W base of Davis Mountain shield volcano and the SW end of Wickup Reservoir.  The two S flows are in a flat area straddling Crescent Creek between Hamner and Odell Buttes.  The middle lava flow erupted from a small, breached cinder one on the lower S flank of Hamner Butte.  It is dated 4.7 ka.  The S flow erupted from a cone at the ENE base of Odell Butte.  All of these lava flows are thought to be similar in age. 

Cinnamon Butte

Cinnamon Butte is a group of young, forested cinder cones located 89 km SW from Newberry.  The group includes Cinnamon Butte, Thirsty Point, Kelsay Point and their associated lava flows.  The cones are generally aligned along a WNW trend.  They have well preserved craters.  The lava flows are unglaciated, passing through gaps in moraines left from the most recent glaciation, meaning they are no older than 15 ka.  They are covered with 6.8 ka Mount Mazama Ash erupted during the creation of nearby Crater Lake (29 km S).  There are other, older cinder cones and domes in the area.  The entire complex is W of the crest of the Cascades. 

China Hat – East Butte

China Hat and East Butte are a pair of rhyolite domes located 16 km ESE from Newberry.  They date 800 and 870 ka respectively.  It is thought to be a side vent of Newberry, it is older than the Newberry Caldera which dates around 500 ka.  Wiki notes that a nearby road is a favorite location for law enforcement targeting speeders. 

Quartz Mountain

Quartz Mountain / Quartz Butte is a dome complex located some 28 km ESE from Newberry.  Activity here dates 1.1 Ma and erupted silica (rhyolites?).

Devil’s Garden

The Devils Garden lava field is the NW-most of a group of three young looking lava fields 38 km SE from Newberry.  The field is 117 km2 of overlapping pahoehoe lava flows erupted from fissures in the NE part of the field.  The fissure created spatter ramparts and cones on a flat surface surrounding several large kupukas of older rocks.  Some of the spatter cones are up to 30 m high.  There are lava tubes in the field. 

Erupted lavas were very fluid, 0.5 m at the vent thickening to 5 km at the end of the flows.  Total volume is 1.2 km3.  All flows are covered by the Mazama Ash, meaning they are older than 6.8 ka.  The upper end of the flows cover glacial outwash sediments, meaning they erupted after the glaciers retreated some 15 – 13 ka.

Two neighboring lava fields, Lava Mountain and Four Craters erupted around 13 ka.  Devils Garden lavas differ in paleomagnetic direction from the lavas of the two neighboring fields, meaning they were a bit younger, though likely not more than 5 ka.  The lavas are fresh with thin or absent paleosols. 

Squaw Ridge

Squaw Ridge / East Lava Field  / Lava Mountain Lava Field is located some 48 km SE from Newberry.  US BLM carries its name currently as Sq___ Ridge, as it is in the midst of renaming geologic features in its public documents. 

The lava field is the second of a group of three young lava fields located in the High Lava Plain SE from Newberry some 49 km SE from Newberry.  The center of the field is a small shield.  Lava flowed in all directions from the central vent.  The vent is now capped by the Lava Mountain cinder cone.  The field is undated, though thought to be a bit older than 10 ka.  It covers around 81 km2. 

Four Craters

The Four Craters Lava Field is the third of a group of basalt lava fields SE of Newberry in the High lava Plains of central Oregon.  It is located some 61 km SE from Newberry.  Lava flows from four pyroclastic cones aligned along a 4 km NW – SE trending line.  The NW (highest) cone has a well-preserved rim.  Other cones are breached to the W, SE and S respectively.  Lavas and cones date around 13 ka.  The cones rise 75 – 120 m above the flows. 

The older rocks under the field sank slightly creating a shallow graben-like sink 3 km wide extending S into an old lake basin.  Crack in the Ground is a feature that marks the W end of this small volcano-tectonic depression.  It is nearly 9 m deep and over a meter wide.  It is a tension fracture in lava flows over a concealed local fault line located in the SW corner of the Four Craters Lava Field. 

Fort Rock

Fort Rock Volcanic Field is a group of tuff rings, tuff cones and maars in the Fort Rock – Christmas Lake Valley basin 37 km S of Newberry.  The 64 x 40 km basin was occupied by a lake during the last glacial cycle.  Basalts erupted through regional faults through the lake and adjacent highland.  The field is named after Fort Rock, a wave-cut tuff ring breached by erosion.  The Table Rock tuff ring and maar complex is at the SE end of the field.  There are multiple scenic maars located near State Highway 31, the largest road through the region.  Hole-in-the-Ground maar was formed 18 – 13.5 ka.

The floor is 150 m below the original ground level.  The maar is 1,600 m in diameter.  It was built in pulses as access to groundwater varied.  Most of the ejecta from the maar is fairly small, but it did toss some blocks several meters across.  The largest of these ended up nearly 4 km from the maar.  There were at least four major explosive events during the eruption. 

It is a National Natural Landmark and State Natural Area (Oregon State Park) just outside the town of Fort Rock.  Its walls tower over 100 m above the surrounding plain.  One of the largest caches of early Native American artifacts dating 10.5 – 9.2 ka was found inside the tuff ring.     

Newberry Volcano

Newberry is physically the largest volcano in the Cascades with an estimated volume of 120 – 500 km3.  As a shield it tops out only 1,300 m above its surroundings.  Its origins are a bit controversial, with an independent hotspot invoked by some.  It is much more likely to be that it is simply part of the greater Cascades volcanic arc, though located E of the line.  Medicine Lake, some 200 km S and E of the main Cascades volcanic arc is the only other similar volcano to Newberry. 

While Newberry is physically shaped as a shield, it is more correctly described as a composite volcano, with lava flows, pyroclastics and tephras from explosive eruptions interlayered.  Its multiple calderas were created by explosive eruptions rather than subsidence.  The volcano is bimodal, erupting basalts to andesitic basalts and rhyolites.  Flank eruptions are typically basaltic, mostly effusive while central eruptions are typically rhyodacitic and explosive, though there have been effusive eruptions at the caldera and scoria from flank vents.  USGS describes Newberry as the most explosive volcano in the Cascades.  

Depending on your sources, activity at Newberry began 600 – 400 ka.  It was built by several thousand eruptions, eventually reaching a height of 4,300 m, some 500 ka.  The most recent of up to five caldera forming eruptions took place 75 ka.  The two crater lakes and resurgent Paulina Peak, the highest current point on the volcano at 2,425 m formed after that eruption.  Its cone is cut by several local fault scarps. 

Pre-caldera lavas 400 – 75 ka are most voluminous, stretching at least 150 km N and 60 km S of the current caldera.  Post-caldera lavas 75 – 12 ka flowed similar distances from the caldera, though did not cover a similar area.  Post-glacial, pre-Mazama lavas 12 – 7.7 ka erupted mostly S and E of the caldera, though some erupted out of the NW Rift Zone.  Most recent lavas 7.7 ka – present erupted within the caldera and from the NW Rift Zone. 

Vents on the flanks tend to follow the regional NE and NW trends caused by Basin and Range Province extension.  Newberry has more individual flank vents than any other volcano in the Lower 48.  These include cinder cones, domes, rifts and spatter features.  At least 25 vents were active over the last 10 ka.  Most of the cinder cones vary 60 – 120 m high.  Some are up to 150 m high.  Most are nearly 1 km in diameter.  Most have summit craters.  Many of the cones are breached at the base, with the lava flows forming a network of connected lava flows.  There are pahoehoe and a’a lava flows and tubes. 

20 rhyolite domes and lava flows are found along its E, W and S flanks.  East Butte and China Hat domes on the E base of the volcano date 850 – 780 ka.  The McKay Butte on the W flank dates 580 ka.  Paulina Peak is close to the summit, within 5 km of the rim wall. 

The current volcano has a 6 x 8 km caldera at its summit, Newberry Crater.  It is forested, with small parts of it covered by lava flows and pumice deposits.  A large crater lake formed immediately after the 75 ka caldera forming eruption.  Post-caldera activity partly filled the caldera with pyroclastics and lava flows, shrinking the original lake to two smaller lakes, Paulina and East Lakes.  There is a 2 km wide isthmus separating the two lakes.  Central Pumice cone rises 700 m above the lakes centered on the isthmus.  It was formed in an explosive eruption 7 ka. 

The most recent caldera formation removed 150 – 300 m from the overall height.  Multiple caldera forming events created nested calderas, with newer ones smaller than the previous.  The first and largest caldera was formed 300 ka, ejecting 10 km3 of material, the Tepee Draw tuff and ash deposits on the E flank. 

Newberry shows little evidence of glaciation.  While there may have been a few persistent snowfields or small cirque glaciers, there is no widespread glacial scouring found.  This is likely due to it being located in the rain shadow of the Cascades. 

Based on volcanic activity at Newberry over the last 15 ka, future eruptions on the flanks are expected to be basaltic, mostly effusive with cinder cone construction and associated tephras / lapilli.  While effusive, lava flow volumes can be quite large.  Future eruptions in the caldera have the potential to be explosive rhyolite eruptions, with explosive volcanism exacerbated by the presence of the crater lakes and wet sediment layers.  There have been four of these over the last 11 ka, erupting some combination of explosive plume, pyroclastic flow and rhyolite lava flow. 

While lahars are not a significant threat on Newberry due to its relatively gentle slope, any eruption that may eject Paulina Lake from the caldera will create lahar(s) that should most likely impact the valley of Paulina Creek which drains the lake and caldera.  An eruption through the lake or pyroclastic flow into the lake may displace water down the canyon.  There is evidence for one such flood, though its origin is unknown and may be due to a smallish landslide into the lake. 

Crater Lakes

The Newberry Caldera has two small crater lakes, East Lake and Paulina Lake.   They are 50 – 80 m deep and differ in layout, water chemistry and sediment.  Geothermal exploration in the 1980s found a 30 m thick layer of siltstone, mudstone, fine graded beds and debris below the lakes.  This layer is interpreted as the remains of an earlier large caldera lake.  There is an active hydrothermal system in the caldera supporting hot springs and fumaroles.  Both lakes have bubbling hot springs on their shorelines.  There is a single fumarole at Lost Lake near the Big Obsidian lava flow. 

East Lake is smaller, with a surface area of 4.2 km2, maximum depth of 55 m and average depth of 20 m.  Paulina lake has a surface area of 6.2 km2, maximum depth of 76 m and an average depth of 50 m.  The water table in the caldera has multiple aquifers.  East Lake has no outlet.  Paulina Lake can overflow, draining outside the caldera.  Both lakes freeze over Nov – May.  Water levels have fluctuated by 5 m since the 1850s, though seasonal fluctuations are less than 60 cm.

Both lakes have been stocked since 1912 with rainbow, brook and brown trout.  There are crayfish in both lakes.  Fish have high mercury contents.  While the hot springs do contribute some volcanic fluids, gasses and hot waters to lake water, both lakes support healthy bacteria, diatom and crawfish populations.  There is some wind-driven mixing of waters in both lakes. 

Newberry Eruptions

The VOGRIPA database carries the two largest eruptions out of Newberry as a VEI 6.4 290 ka which ejected 25 km3 of rhyolite and a VEI 6.1 62 ka which ejected 12.5 km3.  The older eruption produced the Tepee Draw Tuff and was a caldera forming eruption.  The younger eruption produced the Olema and Paulina tephras.  It is not listed as a caldera forming eruption in the VOGRIPA database.  There are four additional eruptions in the VEI 4.5 – 4.0 ranging 400 ka – 690 AD. 

Over its lifetime, Newberry erupted a number of large basalt flows on its N flank.  These reached the modern towns of Bend and Redmond, filling canyons since eroded by present day Deschutes and Crooked rivers.  These flows extended tens of kilometers from the volcano.  Lava from the most recent of these eruptions 78 ka covered the Bend Area, surrounded the Pilot Butte cinder cone, and filled the Deschutes Riverbed.

Newberry produced a number of Plinian eruptions in addition to the caldera-forming eruptions.  Plumes on these are estimated in the 20 km high range.  The most recent of the caldera-forming eruptions covered tens of thousands of square kilometers with ash, extending to the San Francisco on the Pacific Coast, 800 km SW.  Ash there was a centimeter thick.  Some studies estimate up to 60 explosive eruptions ejecting rhyolite and dacite tephras that are found in Idaho, Utah and N California.  These include the Paulina Creek tephra 55 – 50 ka and the Wono tephra 20 ka.  Wono put ash into W Nevada and E central California.  The most recent of these ejected the Newberry pumice and the Big Obsidian lava flow 690 AD. 

Newberry erupted at least 12 times 12 – 7 ka, accumulating a couple meters of ash on the flanks of the volcano.  This ash covered many of the lava flows on the flanks of the volcano.  Six of these were notable.  The South Obsidian eruptive episode 12 ka extruded an obsidian dome and obsidian flow (rhyolite) from a vent along a caldera ring fracture in the SE part of the caldera.  It was quickly followed by the East Rim eruptive episode, 11.2 ka, a basaltic eruption from a fissure on the E rim of the caldera.

The Interlake eruptive episode was a series of rhyolitic eruptions beginning 7.3 ka.  These erupted through East Lake producing widespread phreatomagmatic tephras, obsidian flow, a large pumice cone (Central Pumice Cone) and several small pumice cones.  This episode lasted around 200 years.  Over the last 7 ka, there were seven individual rhyolitic eruptions from separate vents. 

The Northwest Rift eruptive episode started 7 ka, erupting basaltic andesitic lavas from fissures on the N and S flanks.  The East Lake eruptive episode took place 3.5 ka, eruptive obsidian flows and pumice deposits in the caldera from ring fractures near East Lake.  The final and most recent eruptive episode was the Big Obsidian episode.  We will take a look at the NE Rift and Big Obsidian in more detail. 

Newberry has a long history of silicic pyroclastic volcanic eruptions, producing at least 40 and likely more than 50 rhyolitic and dacitic tephra producing eruptions over the last 500 ka.  At least 13 tephras erupted over the last 10 ka.  Only three of these, the E Lake tephra, tephra from the Central Pumice cone, precursor ash from the Newberry Pumice, Newberry Pumice and Paulina Lake ash flow are recognized outside the caldera.  Only the Newberry Pumice extends more than a few kilometers from the caldera. 

Study of earlier tephra layers concentrated almost exclusively outside the caldera.  If the pattern of eruptions older than 10 ka continued, there may very well have been a large number of smaller eruptions confined to the caldera for every identified larger one.  Extensive erosion and burial of older deposits on the flanks may limit the number of tephras observed, leading to underestimation of the actual number of tephra producing eruptions. 

640 AD Big Obsidian Eruption

The most recent eruption was the Big Obsidian lava flow event.  It began explosively with a plume that deposited the 0.42 km3 Newberry Pumice.  The plume collapsed and emplaced a small pyroclastic flow.  The final phase was effusive, extruding the 0.1 km3 Big Obsidian Flow.  The 25 cm isopach extends a full 60 km E.  The eruption deposited juvenile pumices as lapilli, followed by obsidian pyroclasts.  There were lithics ejected from the vent during the later stages of the eruption.  These deposits cover yellow-orange deposit from the 7.7 ka Mount Mazama eruption. 

The Newberry Pumice was the result of an initial sub-Plinian eruption that transitioned into a Vulcanian eruption.  It proceeded in two phases, which deposited two units, Lower (0.31 km3) and Upper (0.11 km3).  Plume height for both phases is estimated at 18 km.  They are separated by a thin ash layer, a change in obsidian textures, and a change in size of clasts.  Both layers were deposited generally NE, though there was a change in wind direction, more N for the Upper unit.  The ash layer separating the two units is thought to be a pause between two explosive phases of the eruption.  There were pyroclastic flows associated with the Upper unit.  The second phase proceeded in pulses as the conduit was repeatedly sealed by a dense plug that was reopened and partly emptied during each explosion. 

The final Vulcanian explosion started the transition of the eruption from explosive to effusive.  As the conduit narrowed, ascent velocity increased resulting in larger clasts as the explosion excavated more conduit wall material.  There was a marked increase in obsidian content of all sizes. 

The Paulina Lake ash flow erupted after the Newberry Pumice.  It is found on exposures on the S shore of Paulina Lake and the S caldera rim.  It is poorly sorted ash and lapilli.  The Big Obsidian Flow was the final phase of the eruption.  It is 1.8 km long and over 20 m thick in places.  All phases erupted chemically similar magmas.  The eruption proceeded similarly to those of 2008 and 2011 – 2012 Cordon Caulle, erupting crystal poor rhyolites. 

The recent rhyolite eruptions produced obsidian flows with high quality glass that attracted prehistoric natives.  They quarried obsidian, producing unfinished tools for transport and trade.  Most of this took place in the caldera, though McKay Butte on the flank was an important initial source for obsidian.  It was quarried before the natives discovered obsidian in the caldera. 

Northwest Rift Zone Eruption

The 7 ka Northwest Rift Zone (NWRZ) eruption produced multiple lava flows from a variety of vents including cinder, spatter cones and fissures.  There may have been more than one closely spaced episode.  Eruptions proceeded as vigorous Strombolian with significant tephra plumes to low energy Hawaiian-style eruptions.  Lava flows traveled 32 km N-S.  The N flow blocked the Deschutes River upstream from Bend, changing its course.  Future similar eruptions may have significant impact for residents of Bend and other central Oregon communities.  All NWRZ lavas and airfalls cover the 7.7 ka Mount Mazama ash. 

The NWRZ flows are mostly treeless and young in appearance, ranging from pahoehoe to ‘a’a and blocky lavas.  There are 12 informally named flows, one unnamed flow and the E Lake Fissure.  Two other flows previously included as part of the NWRZ eruption at Devils Horn and The Dome predate the Mazama Pumice and are no longer included as part of the eruptive sequence. 

Total area covered by nearly 0.9 km3 of lava is 68 km3.  Vents range 1,375 – 2,260 m in elevation.  Over 90% erupted below 1,750 m from the NW 11 km of the rift zone.  Two cones, Lava Butte and Mokst Butte erupted in the NW part of the rift, producing the two largest lava flows, 80% of the total volume.  The northernmost flow, Lava Butte is one of the largest at 0.3 km3, and blocked the Deschutes River.

With one exception, all vents in the S portion of the rift are spatter vents.  The single central vent of the Surveyors flow in the far S end of the NWRZ can be considered a small cinder cone.  Spatter vents in the NW part of the rift zone only produced very small volume lava flows.  The NW portion of the zone is widest, spanning multiple fissures across 10 km.  In the S, the vent locations are much narrowly grouped, only 1 km wide.  There is a 10 km break in active fissures in the S part of the zone.  There is no difference in age between vents and fissures in the N and S. 

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Tephras from Lava Butte indicate its eruption took place in at least three explosive pulses early in the eruption.  Eruptions like those from the NWRZ that produced multiple vents and lava flows may persist intermittently for years to decades.  Multi-vent eruptions are common at Newberry, and the opening of a single first vent does not preclude additional vents from opening.  Future similar eruptions from Newberry will present a threat to those in Bend and surrounding communities.

Eruptions from the NWRZ created two of the more popular features on Newberry, the Lava River Cave and the Lava Cast Forest. 

Geothermal

Newberry was extensively studied as a prospective geothermal energy source 1970s – 1980s.  Creation of the Newberry National Volcanic Monument in 1990 stopped all geothermal exploration in the caldera and the NWRZ.  Research then shifted to the W flank of the volcano, outside the protected area, where high temperatures and enhanced hydrothermal alteration of volcanic rocks are found via boreholes.  This heat is from intrusive rock.  Sadly, there has been little recent work toward understanding the volcanoes hydrothermal system.

Given Newberry’s 500 km3 volume, it would seem that a great deal of heat is available to support geothermal energy.  Yet, there are only two mildly hot springs in the caldera.  Exploratory drilling into the caldera found heat consistent with magma as close as 2 km below the surface, but not a lot of water.  There is a fracture zone in the upper 500 m of the caldera rim that may be a pathway for groundwater and probably has altered rocks. 

Exploratory drilling for geothermal exploration in 1995 – 1996 to a depth of 3,000 m on the W flank found heat but no fluids.  That project was shelved.  Another attempt was made in 2012.  This time around, water was injected into the dry well to see if it could be heated and returned to the surface in sufficient quantity to power geothermal electric generation.  Many continue to believe Newberry is the best geothermal candidate in the Pacific Northwest. 

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Tectonics

Given that Newberry is 80 km SE from Belknap and the regional volcanism described in that post, the regional tectonics are similar, so we will repeat much of what we published in that post, albeit in a slightly truncated form. 

Newberry is near the propagating tip of a crustal melting anomaly that is progressing W across Oregon over the last 15 Ma, penetrating the Cascades over the last 10 ka.  The N margin of the extensional Western Basin and Range Province meets the Cascade arc triggering high vent density.  The westward propagation of the neighboring Basin and Range Province into W Oregon powers volcanism at Newberry.  Crust under Newberry thins to 35 km from 50 km at neighboring Three Sisters.  Its unique magmas are attributed to shallow depth of the subducting plate. 

An alternate, highly speculative question would be to ask if this extensional regime is related to the N and W propagation of Walker Lane rifting as it continues to carve the Sierras and W California from North America.  Is this a distinction without a difference?  Unknown, though more correctly, perhaps.  My completely uneducated guess would be that this may be an alternate explanation, though I have no idea when or where the alternate explanation becomes simply the official explanation using different words.  Should be a fascinating journey.

One of the things I learned researching this post was the widespread outbreak of calderas in Oregon.  There are multiple reasons for the outbreak.  In the N part of the state, we have the impact of the Yellowstone hotspot and whatever powered the Columbia River Basalt.  Earlier activity, like that in NV, UT and CO were driven by flat slab subduction of the Farallon Plate 30 – 20 Ma.  More recent caldera activity has been driven by extension of the Basin and Range Province and penetration of the Walker Lane into the state.  This tectonic mess deserves a dedicated post if for no other reason than the number of calderas in this part of the US.  I expect there will be one of those in the future. 

Conclusions

Newberry is a huge, previously active, bimodal volcano active for at least 500 ka.  Most recent eruptions were explosive rhyolitic eruptions from the caldera a mere 1,300 years ago.  The most recent flank eruption 7.7 ka were basaltic andesitic from the NERZ.  Eruptive products were mostly effusive, though there were scorias and lapilli.  While the volcano does not have a particularly vigorous hydrothermal system, this is more due to lack of meteoric water than a lack of subsurface heat.  The most fortunate thing about Newberry is the relatively small population in close proximity to it. 

Additional information

Newberry Volcano – Wiki

Newberry National Volcanic Monument – Dechutes NF, USDA, USFS

Newberry – Smithsonian GVP

Newberry – USGS

Newberry National Volcanic Monument – Visit Bend.com

Newberry Volcano – Central Oregon’s Sleeping Giant, USGS, 2011

Explore the wonders of Newberry National Volcanic Monument, E Garvin, May 2015, Travel Oregon

Newberry National Volcanic Monument – by geologist Jason McClaughry, Oregon Secretary of State

Electrical structure of Newberry Volcano, Oregon, Fitterman, et al, USGS Open File Report 88-245, 1988

A field guide to Newberry volcano, Oregon. Jensen, et al, Field Guides 2009; 15; 53-79

Volcano hazards at Newberry volcano, Oregon, Sherrod, et al, Open File Report 97-513, USGS, 1997

Newberry volcano, Oregon:  a Cascade Range geothermal prospect, McLeod & Sammel, Oregon Geology, Vol 44, No 11, Nov 1982

Plinian eruptions at Glacier Peak and Newberry volcanoes, United States:  Implications for volcanic hazards in the Cascade Range, Gardner, et al, Sept 2015

Post-Mazama northwest rift zone eruption at Newberry volcano, Oregon, Mckay, et al, Field Guides 2009; 15; 91-110

The pivotal role of Vulcanian activity in ending the explosive phase of rhyolitic eruptions:  the case of the Big Obsidian Flow eruption (Newberry volcano, USA), Trafton & Giachetti, Oct 2022

A tale of two lakes:  the Newberry volcano twin crater lakes, Oregon, UISA, Lefkowitz, et al, Nov 2016

Oregon Geology, Oregon Department of Geology and Mineral Industries, Vol 69, Number 1, Fall 2009