Newberry Volcano

Newberry Volcano 7,985 ft (2,434 m) high is large shield volcano located 40 miles (60 km) east of the Cascade Range and about 20 miles (30 km) southeast of Bend, Oregon. It is not a typical shield volcano in that, in addition to erupting basaltic lavas, it also has erupted andesitic and even rhyolitic lava.

The volcano is 20 miles (30 km) in diameter, has an approximate volume of 80 mile³ (330 km³), and it possesses a large oval-shaped caldera four by five miles in diameter, called the Newberry Caldera. Within the caldera there are two lakes (Paulina Lake and East Lake) many cinder cones, lava flows, and obsidian domes.

A deep gash in the northern caldera wall, dubbed The Fissure, is the end of a 29 mile (47 km) long series of fractures called the Northwest Rift Zone. Approximately 6100 years ago, fissure basalt flows erupted from the rift and covered part of Newberry's northwest flank.

A great deal of volcanic activity has occurred on Newberry's shield, which itself has one of the largest collections of cinder cones, domes, lava flows, and fissures in the world (local residents call these parasitic vents the "Paulina Mountains", as if they were their own mountain range). Most of the cinder cones are 200 to 400 ft (60 to 120 m) high and have shallow saucer-shaped summit craters. They are typically surrounded by basalt or andesite that erupted from their bases, forming large lava beds. There are also about 20 rhyolite domes or fissures on the eastern, southern, and western flanks. Larger examples include McKay Butte on the west flank (580,000 years old), China Hat (780,000 years old) and East Butte (850,000 years old) on the far eastern base.

During the late Pleistocene and Holocene there have been six eruptive episodes; four rhyolitic (east half of the caldera) and two basaltic (on the flanks).

• South Obsidian Eruptive Episode: An estimated 12,000 calendar yrs ago, an obsidian dome and related obsidian flow erupted in the southeast part of the caldera.
• East Rim Eruptive Episode: About 11,200 calendar yrs ago (10,000 C14 yrs B.P.), mafic cinders, scoria, spatter, and lava flows erupted from a fissure on the east rim of the caldera.
• Interlake Eruptive Episode: A series of rhyolitic eruptions began in the caldera approximately 7,300 calendar yrs ago (6,200 C14 yrs B.P.). They produced a widespread phreatomagmatic pumiceous tephra deposit, obsidian flows, large and small pumice cones, and a pumice ring. This eruptive episode probably lasted for about 200 years.
• Northwest Rift Eruptive Episode: About 7,000 calendar yrs ago (6,100 C14 yrs B.P.), basaltic andesite lava and cinder cones erupted from extensive fissure vents on the northwest and south flanks of Newberry. Spatter and cinders also erupted from a fissure on the north caldera wall. The lava flows range up to 9 km long and are more voluminous at lower elevations. This eruptive episode probably lasted for less than 50 years.
• East Lake Eruptive Episode: About 3,500 yrs ago, obsidian flows and associated pumice deposits in the caldera erupted from caldera ring fractures.
• Big Obsidian Eruptive Episode: About 480 A.D. (1,470 calendar years B.P.), a 3-part sequence of rhyolitic eruptions began, which included an air-fall tephra, ash-flow tephra, and an obsidian flow, from a common vent at the base of the south caldera wall. The initial Plinian eruption 480 A.D. (1,580 C14 yrs B.P.) produced the Newberry pumice fall deposit which blanketed the east flank of the volcano and areas to the east. About 210 yrs later the Paulina Lake ash flow (1,310 C14 yrs B.P.) spread from near the south caldera wall to Paulina Lake. The final phase of the eruption produced the Big Obsidian Flow which covers 2.8 sq km.

Newberry's highest point is located 1500 ft (450 m) above the southern caldera floor on Paulina Peak, which is just one peak on the caldera rim. The volcano's south flank descends into the basaltic flatlands of central Oregon.

During the Apollo program, parts of the volcano that resemble the Moon's surface were used to train astronauts.

Geology

Newberry Caldera has existed possibly as long as 500,000 years, when the cone of the volcano is thought to have first collapsed. Subsequent caldera-forming collapse events have further deepened the caldera, but volcanic material and lakebed sediments have largely filled in much of this depth (see Newberry Caldera for details).

See also

• Newberry National Volcanic Monument,
• Map of Newberry Volcano and surroundings

Reference

• USFS web page about Newberry (retrieved from Google Cache, July 2, 2005; PD source)
• Fire Mountains of the West: The Cascade and Mono Lake Volcanoes, Stephen L. Harris, (Mountain Press Publishing Company, Missoula; 1988) ISBN 0-87842-220-X