Newberry Volcano

Newberry Volcano

Newberry Volcano is a large shield volcano located 40 miles (64 km) east the Cascade Range and about 20 miles (32 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.

Newberry Volcano was named for Dr. John Strong Newberry, who explored central Oregon for the Pacific Railroad Surveys in 1855.

The volcano is 20 miles (32 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 pyroclastic cones, lava flows, and obsidian domes.

A deep gash in the northern caldera wall, dubbed The Fissure, is the end of a 29 miles (47 km) long series of fractures called the Northwest Rift Zone. Approximately 6,100 years ago, fissure basalt flows erupted from the rift and covered part of Newberry's northwest flank.

Geology

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", thinking of them as a separate 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. On the northwest flank of the volcano, Lava Butte, located next to Highway 97 south of Bend, is a good example of this kind of cinder cone and lava bed. 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 km².

Newberry's highest point is located 1,500 feet (460 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.

Caldera

Map of Newberry Volcano and surroundings

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.

Within the caldera there are two lakes (Paulina Lake and East Lake), many cinder cones, lava flows, and obsidian domes. The land area of the caldera is heavily forested except in areas where there are more recent volcanic flows and features. Paulina Lake is drained by Paulina Creek, which passes through a narrow gorge through the western part of the caldera rim. East Lake does not have a known outlet and is thus 40 feet (12 m) higher than Paulina Lake. 6700 year-old basalt flows separate the two caldera lakes. Rising 700 feet (210 m) above this flow is the Central Pumice Cone.

Both lakes have hot springs and drilling in 1981 found that temperatures in the caldera reach 280 °C (540 °F) at 3,057 feet (932 m) below the caldera floor. This is the highest temperature ever recorded at a dormant Cascade volcano (higher than even The Geysers of California, the world's largest producer of geothermal power).

Newberry has had a caldera for possibly as long as 500,000 years, when a large Plinian Eruption (on the VEI scale) sent so much pyroclastic material gushing from its vent that the then emptied magma chamber collapsed. This was repeated for several eruptions; each forming a slightly smaller caldera. The half-million year old (estimated) Teepee Draw tuff covers much of the volcano's shield and was from an eruption with an estimated volume of 10 cubic miles (42 km²). This is thought to be the first in a series of caldera-forming eruptions that issued from Newberry's main vent system. One of the later layers is cut by Newberry's only stream, Paulina Creek.

Subsidence of the caldera through time has been partly offset by the deposition of tephra, lava flows, and lake sediment. The USGS has drilled 3,057 feet (932 m) below the present surface of the caldera and has found that:

• First 950 feet (290 m): Dominated by airfall pumice, obsidian flows, and under-water erupted ash.
• 950 to 1180 feet (290 to 363 m): Lake-bottom sediments.
• 1180 to 1640 feet (363 to 505 m): Thick layers of pumice-rich ash and breccia.
• 1640 to 2449 feet (505 to 754 m): Rhyolitic to dacitic lava flows.
• 2449 to 3057 feet (754 to 941 m): Basalt to basaltic-andesite lava flows and breccia.

There are several large flows of obsidian in the caldera, one of which, Big Obsidian Flow, was created around 1400 years ago and is thus the most recent caldera eruption. This particular flow erupted from a vent or fissure near the southern wall of the caldera and partially engulfed the Lost Lake pumice ring.

Hotspot

Newberry Volcano is very unusual, in that it has erupted such diverse lava types. Unlike most other volcanoes, Newberry has erupted lava with widely varying silica content, composition, temperature, viscosity, and explosiveness. Some variation is found with all volcanoes, but Newberry deviates more than most. The exact reason for this is unknown, but it appears that the volcano is the result of a hotspot and not part of the Cascade Range.

Newberry is located at the northwest end of the Brothers Fault Zone, a dense cluster of faults that runs northwest from the southeastern corner of Oregon to the High Cascades. Some scientists associate these faults with the Columbia River Basalt Group, but little evidence for a direct correlation exists. The hotspot chain has produced a train of volcanic features beginning approximately 15-16 million years ago, and continuing into the present geothermal activity at Newberry. The train is very steady, with a new feature being formed roughly once every two million years. They are generally assumed to be part of a hotspot track, but one that is not associated with mantle plumes. Normally, it is believed, hotspots produce a chain of volcanoes as a plate moves across a column of superheated rock originating from deep within the earth. These are called mantle plumes. However, the Newberry Hotspot Track runs roughly 120° to the movement of the North American Plate. Clearly, a different process must be at work. Several alternate models have been proposed, including subduction counterflow, gravitational flow along the base of the lithosphere, and extension of the Basin and Range. Subduction counterflow is a back current generated in the lithosphere by a subducting plate. Gravitational flow along the base of the lithosphere is like reverse water flow on the surface, in which the asthenosphere flows up along mountain roots.

See also

• Newberry National Volcanic Monument
• Cascade Volcanoes

References

• "USFS: Newberry Volcano". Retrieved 2008-03-23.
• Harris, Stephen L. (1988). Fire Mountains of the West: The Cascade and Mono Lake Volcanoes. Missoula: Mountain Press Publishing Company. ISBN 0-87842-220-X.

External links

• U.S. Geological Survey Geographic Names Information System: Newberry Volcano
• "USGS Cascades Volcano Observatory". Retrieved 2008-03-23.