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Features of Newberry Caldera

North-facing view of the 4-by-5 mile Newberry Caldera from the top ...
North-facing view of the 4-by-5 mile Newberry Caldera from the top of Paulina Peak (7,984 feet - the volcano's summit). The two lakes, Paulina Lake (6,331 feet) on the left, and the slightly higher East Lake on the right are fed by snowmelt, precipitation, and hot springs from depth. The 7,084-foot-high Central Pumice Cone sits between the lakes. The mostly treeless Big Obsidian Flow, youngest lava flow on the volcano (1300 years old) lies surrounded by forest south of the lakes. (Credit: Jensen, Robert. Public domain.)

The present 6.5 by 8 km (4 by 5 mi) caldera at Newberry Volcano's summit formed about 75,000 years ago by a major explosive eruption and collapse event. This was the most recent of at least three caldera- forming eruptions that lofted pumice and ash (tephra) high into the air and spread pyroclastic flows across the volcano's surface. Subsequent lava flows have partly buried the deposits from this eruption, but one exposure can be seen at Paulina Creek Falls, where a deposit of pyroclastic flow and fall material was so hot that ash and pumice particles were welded together and then cooled into solidified rock.

Before formation of the caldera, Newberry’s summit was 150 to as much as 400 m (500 to 1,000 ft) higher than present-day 2,434-m (7,986-ft) Paulina Peak. Once the caldera was formed, more eruptions began to fill it with lava flows, and lava also erupted at numerous sites outside the caldera, covering much of the volcano’s north and south flanks.

Today, Newberry caldera holds two beautiful lakes, Paulina Lake and East Lake, popular for fishing, boating, swimming, and camping. Both caldera lakes have hot springs with temperatures as high as 135 degrees Fahrenheit. In 1987, temperatures higher than 500 degrees Fahrenheit at a depth of 900 m (approximately 3,000 ft) were found in a U.S. Geological Survey drill hole in the center of the caldera. These temperature measurements indicate that an active magma system lies beneath Newberry Volcano.