The gentle slopes in this photo belong to a shield volcano located at the meeting place of three major landscape regions in central Oregon: the Oregon Lava Plateau, the Basin and Range, and the Cascade Range. All three regions involve various forms of volcanic eruptions, and at Newberry Volcano the magma-generating processes have come together to produce the largest shield volcano in the Pacific Northwest.

If you look closely, you can see some smaller hills on the flanks of Newberry Volcano. Each of these hills is a cinder cone formed where mafic magma charged with gas erupted as a fountain from a small vent. The "cinders" are volcanic blocks, bombs, and scoria thrown into the air by the small pyroclastic eruptions. They fall back to the ground around the vent, building up into a cinder cone.

Obsidian Flow

This is the Great Obsidian Flow, a pile of volcanic glass that erupted as lava from the side of Newberry Crater. Newberry Crater is five miles wide and is the caldera of Newberry Volcano. Most of Newberry Volcano is of made basalt, which is much more mafic and poor in silica than the felsic, silica-rich obsidian erupted in the crater. Late in the history of the volcano, after it had built its shield from thousands of basalt flows, it erupted felsic ash and lava from cracks in its summit caldera. This may be because the heat of all the earlier mafic magma caused the continental crust beneath the volcano to melt, and molten continental crust forms felsic magma. Select the image to see a larger view. Use your browser's back button to return to this page.

Obsidian Chunk

This photo shows a close-up of a piece of obsidian from the Great Obsidian Flow. Obsidian is volcanic glass. The characteristic glassy luster and conchoidal fracture of obsidian appear in the photo. Conchoidal fracture is the tendency to break into curving, sharp-edged ridges, just as a thick piece of standard glass breaks. Select the image to see a larger view. Use your browser's back button to return to this page.

Obsidian does not qualify as a mineral because it lacks a crystal lattice structure. Two factors prevent development of a crystal lattice structure. There must be hardly any water dissolved in the magma and the lava must undergo rapid cooling. The presence of water in lava speeds the rate at which atoms can move around to join into crystal lattice structures-to crystallize into minerals. Lack of water in the lava slows the atoms, making it difficult for them to join together in an organized way.

Slow cooling allows enough time for the atoms to organize into crystal lattices. If the cooling rate is too rapid, as it was for the Great Obsidian Flow lava, the lava simply quenches into atoms bonded together in unorganized patterns. The result is glass.

Lava Butte

The cinder cone in this photo is Lava Butte near Bend, Oregon, about 15 miles north of Newberry Volcano. This pile of loose material shows the typical shape of a cinder cone--steep-sided, but small enough that people who like to hike could climb to the top in a few minutes. The steep trail up the side of the cone has been created by such people. Select the image to see a larger view. Use your browser's back button to return to this page.

The boulder rubble in the foreground is the top of a lava flow that came out of the base of Lava Butte, after the magma ran out of gas.

Spatter Cone

In the foreground is part of a small spatter cone. It is on the back side of Lava Butte (see previous picture). A spatter cone is a mound of lava formed when gas causes the lava to heave upward and spatter around the vent in liquid blobs, which pile up into a spatter cone. These blobs indicate that the eruptions that formed Lava Butte were becoming depleted in gas. The reduced amount of gas in the magma caused the style of eruptions to change from pyroclastic eruptions (driven by gas pushing out of the lava) to lava eruptions (liquid flowing on the ground). Select the image to see a larger view. Use your browser's back button to return to this page.

Mt. Bachelor, a composite cone volcano of the Cascade Range in central Oregon, is in the distance. Its profile with sides much steeper than those of Newberry Volcano is what many people think of when they picture a volcano.

Glossary terms that appear on this page: shield volcano; cinder cone; obsidian; caldera; basalt; mafic; felsic; silica; conchoidal fracture; crystal lattice structure; volcanic block; volcanic bomb; scoria; pyroclastic; composite cone