Newberry Volcano - Caldera

Caldera

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 lake-bed 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 often 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 40 feet (12 m) higher than Paulina Lake. Basalt flows 6700 years old 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, hotter than even The Geysers of California, the world's largest producer of geothermal power.

The caldera was formed when a large Plinian Eruption 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 km3). 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 air-fall pumice, obsidian flows, and under-water erupted ash.
• 950–1,180 feet (290–360 m): Lake-bottom sediments.
• 1,180–1,640 feet (360–500 m): Thick layers of pumice-rich ash and breccia.
• 1,640–2,449 feet (500–746 m): Rhyolitic to dacitic lava flows.
• 2,449–3,057 feet (746–932 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.