when did the largest swarm of earthquakes at long valley take place
May 1980
title: Long Valley Caldera text: have prominent moraines. In May 1980, a strong earthquake swarm that included four Richter magnitude 6 earthquakes struck the southern margin of the Long Valley Caldera. It was associated with a , dome-shaped uplift of the caldera floor. These events marked the onset of the latest period of caldera unrest that is ongoing. This ongoing unrest includes recurring earthquake swarms and continued dome-shaped uplift of the central section of the caldera accompanied by changes in thermal springs and gas emissions. After the quake, another road was created as an escape route. Its name at first was proposed as the "Mammoth title: Long Valley Caldera text: Long Valley Caldera Long Valley Caldera is a depression in eastern California that is adjacent to Mammoth Mountain. The valley is one of the Earth's largest calderas, measuring about long (east-west), wide (north-south), and up to deep. Long Valley was formed 760,000 years ago when a supervolcanic eruption released very hot ash that later cooled to form the Bishop tuff that is common to the area. The eruption emptied the magma chamber under the area to the point of collapse. The second phase of the eruption released pyroclastic flows that burned and buried thousands of square miles. Ash from this title: Long Valley Caldera text: other matter, was blown as far as into the air where winds distributed it as far away as eastern Nebraska and Kansas. The eruption initially produced a caldera deep. However, much of the ejecta went straight up, fell down, and filled the initial caldera about two-thirds full. Subsequent eruptions from the Long Valley magma chamber were confined within the caldera with extrusions of relatively hot (crystal-free) rhyolite 700,000 to 600,000 years ago as the caldera floor was upwarped to form the resurgent dome followed by extrusions of cooler, crystal-rich moat rhyolite at 200,000-year intervals (500,000, 300,000, and 100,000 years ago) title: Long Valley Caldera text: began to collect several miles below the surface. Volcanic activity became concentrated in the vicinity of the present site of Long Valley Caldera 3.1 to 2.5 million years ago with eruptions of rhyodacite followed by high-silica rhyolite from 2.1 to 0.8 million years ago. After some time, a cluster of mostly rhyolitic volcanoes formed in the area. All told, about were covered by lava. All but one of these volcanoes, 1–2 million year old Glass Mountain (made of obsidian), were destroyed by the major (volcanic explosivity index (VEI) 7) eruption of the area 760,000 years ago, which released of material title: Mono–Inyo Craters text: Craters and eruptions 5,000 to 500 years ago formed the Inyo Craters. Lava flows 5,000 years ago built the Red Cones, and explosion pits on Mammoth Mountain were excavated in the last 1,000 years. Uplift of Paoha Island in Mono Lake about 250 years ago is the most recent activity. These eruptions most likely originated from small magma bodies rather than from a single, large magma chamber like the one that produced the massive Long Valley Caldera eruption 760,000 years ago. During the past 3,000 years, eruptions have occurred every 250 to 700 years. In 1980, a series of earthquakes