Newberry Caldera
From Wikipedia, the free encyclopedia
Newberry Caldera is the caldera on Newberry Volcano, a shield volcano in central Oregon that is part of the Cascade Range. The caldera is oval-shaped and four by five miles (6 by 7 km) in diameter (with its major axis trending east-west).
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 (13 m) higher than Paulina Lake. 6700 year-old basalt flows separate the two caldera lakes. Rising 700 feet (230 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 (510 degrees Fahrenheit) at 3057 feet (941 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).
[edit] Geology
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 950 meters (3000 ft) 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.
[edit] Reference
- 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
