The broad depression of Long Valley Caldera that we see today is much shallower and a little larger in diameter than it was immediately after its formation about 760,000 years ago. Whereas the caldera was floor was initially 2,000-3,000 m deep, now the highest part of the caldera rim is only about 1,000 m above the floor. The caldera was partially filled by pyroclastic flows and tephra during the catastrophic eruption and also by many subsequent episodes of volcanic activity. The original topographic boundary of the caldera walls has been enlarged by landslides, glaciation, and rapid erosion. For example, geologists estimate the modern-day east caldera wall is 3-4 km farther east than its orginal boundary.