Since the enormous explosive eruption formed the caldera about 760,00 years ago, hundreds of smaller eruptions have partially filled the initially deep depression. Within the first 100,000 years, explosive eruptions, followed by many thin fluid obsidian lava flows, produced deposits of tephra and lava flows that form a layer 100-500 m thick on top of the Bishop Tuff. At the same time, these deposits were pushed upward by the intrusion of molten rock into the magma reservoir beneath the caldera, forming the resurgent dome. Then, after a period of quiet lasting about 100,000 years, three new periods of volcanic activity each erupted four or five steep domes and lava flows around the low margins of the resurgent dome. Scientists refer to these flows as the moat rhyolites, and they occurred about 500,000, 300,000, and 100,000 years ago.