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Resurgent Dome in the Long Valley Caldera, California

The resurgent dome is a broad area of the central caldera floor that was pushed upward within 100,000 years or less of the caldera-forming eruption 760,000 years ago. This uplift was caused by upward pressure related to the intrusion of molten rock into the magma reservoir beneath the caldera. The resurgent dome is made of layers of lava flows, tephra, and pyroclastic flows that were erupted onto the caldera floor soon after the caldera formed. The uplift arched and faulted these volcanic rocks to form a central highland area about 10 km (6.2 mi) in diameter and as high as 500 m (1,640 f) above the surrounding caldera floor.