Newberry Volcano in central Oregon is part of the Cascade Range of America's Pacific Northwest. The presence of Newberry Volcano, like the other Cascade volcanoes, is the result of the Juan de Fuca Plate subducting beneath the North American Plate along offshore Oregon & Washington State. Newberry Volcano experienced a large eruption and has collapsed, forming a large caldera, now partially occupied by two lakes (Paulina Lake & East Lake).
(Satellite photo provided by TerraMetrics & DigitalGlobe & Google Earth)
Lava Butte is an obvious & decent-sized cinder cone on the western side of Rt. 97, about 10 miles SSW of Bend, central Oregon, USA. It is one several volcanic features associated with a NNW-SSE trending fracture system extending from Newberry Volcano to the south.
Basalt & vesicular basalt aa lava flows extend to the west & northwest from Lava Butte. These were erupted in about 5075 B.C. (~early Holocene).
Lava Butte Cinder Cone is the rounded structure near the lower right corner. The brown sheet extending toward the center & upper right of photo are the ~5075 B.C. lava flows. (Satellite photo provided by TerraMetrics & DigitalGlobe & Google Earth)
Lava breach on the southern side of the Lava Butte Cinder Cone. Lava erupted from a fissure developed in the flanks of the cinder cone, rather than from a vent at the top.
~5075 B.C. basaltic aa lava flow.
Basalt & vesicular basalt lava, ~5075 B.C. eruption of Lava Butte Cinder Cone.
Lava Cast Forest
Fossils are only common in sedimentary rocks. They are scarce in metamorphics, and are exceedingly rare in igneous rocks. Famous examples of fossils in igneous rocks include a rhinoceros in the Columbia Plateau Flood Basalts (Blue Lake, Washington State) and some trees in the basalt lavas of the Hawaii Hotspot.
Another spectacular place for seeing fossils in igneous rocks is Lava Cast Forest, central Oregon. Many upright & horizontal tree molds are preserved in the Lava Cast Forest Flow (an aa lava flow consisting principally of vesicular basalt and some scoriaceous basalt), which erupted about 5260 B.C. from a fissure ~7 miles north-northwest of Newberry Volcano. [these tree molds really aren't fossils, since they aren't >10,000 years old, but that's a minor quibble]
Location: area of 43° 48' 54" North, 121° 17' 11" West.
Some of the tree molds are suspiciously rounded, and resemble large drill holes. The trees represented by the molds were likely ponderosa pines, which are still common in central Oregon. Only occasional carbonized traces of the original trees remain. During the original eruption, lava piled up against the upstream side of the trees - these lava pile-ups are still evident, and the upstream lava flow direction is readily discernible.
Basaltic aa lava of the Lava Cast Forest Flow (erupted ~5260 B.C.).
Looking down into a vertical tree mold in the Lava Cast Forest Flow.
Another vertical tree mold, with a lava pile-up at the back (indicating the lava flow's upstream direction).
A horizontal tree mold in the Lava Cast Forest Flow.
View of the inside of a horizontal tree mold.
This gives a sense of scale for one of the larger upright tree molds. This one has a particularly sizable lava pile-up on the upstream side.
A modern ponderosa pine living between two lobes of the Lava Cast Forest Flow.
BIG OBSIDIAN FLOW
Words and pictures really don't do justice to the Big Obsidian Flow of Newberry Volcano in central Oregon, USA. There's nothing quite like walking on a gigantic pile of black volcanic glass. Erupted in ~700 A.D., this lava flow in Newberry Volcano's caldera is a jumbled mixture of rhyolitic obsidian, rhyolite pumice, vesicular rhyolite, and rhyolite. The obsidian is its most appealing feature, and one has to mind carefully the placement of feet and hands because exceedingly sharp broken glass is everywhere.
Location: southern side of Rt. 21 in the Newberry Volcano caldera, just southeast of Paulina Lake, southern Deschutes County, central Oregon, USA. Area of 43° 42' 15" North, 121° 14' 06" West.
(Satellite photo provided by DigitalGlobe & Google Earth)
Lava flow front of the Big Obsidian Flow (~700 A.D.). The body of water in the foreground is Lost Lake. Looking east.
Flow top of the Big Obsidian Flow.
Large, sharp-edged boulder of flow-banded rhyolitic obsidian.
Making a throne of sharp, irregular obsidian boulders is tricky, but black rock that has been warmed by the Sun is welcome on a chilly, windy day.
World-class piece of rhyolitic obsidian.
I didn't keep it (this is a park).
Lifting a boulder of pumice.
Nice vesiculation on a piece of partially pumiceous rhyolite.
Interesting obsidian-pumice flow banding. This is somewhat the equivalent of flame structures in turbidites. A piece of obisidian (black chunk at right-center) has been picked up and moved around, drawing thin strands of pumiceous & non-pumiceous glass into a convoluted, folded pattern.