<P> Mazama was last active about 4,800 years ago , when an eruption took place near Wizard Island 's eastern base . This eruption took place underwater , and it produced viscous lava that created a rhyodacite lava dome , about 2,400 years after the first period of postcaldera activity . Given that Mazama has had periods of sporadic eruptions for 420,000 years , the United States Geological Survey thinks that it is `` virtually certain '' that Mazama will erupt again in the future . Mazama is considered dormant , but it remains monitored by the United States Geological Survey Cascades Volcano Observatory . Future eruptions would likely take place near the western side of the complex and within the caldera rim ; they could occur underwater . The ejection of lava rich in gas from shallow water could produce huge ash columns , but submarine eruptions at deeper depths may decrease the explosiveness of the event . Nonetheless , the rapid mixing of water and lava could produce dangerous pyroclastic surges , which are more gaseous and less solid than pyroclastic flows . Such flows could pass over topographic barriers , move rock fragments at rapid speeds of 800 feet per second ( 240 m / s ) , and travel several miles from their vent . Mazama is unlikely to produce mudflows far from the caldera , though a nearby vent outside the caldera could erupt and mix with snow . Eruptions are unlikely to produce waves that extend beyond Crater Lake , but powerful explosions could produce tall waves in the caldera . An eruption as explosive as the one 7,700 years ago is unlikely given that it would require larger volumes of magma than are known to be available within the Mazama vicinity . Moreover , landslides could flood adjacent shoreline regions , but they are not likely to induce failure of the caldera 's walls , as they rise more than 500 feet ( 150 m ) above the lake 's surface . Earthquakes from the nearby West Klamath Lake fault zone could reach magnitudes up to 7.0 on the Richter scale , but these only occur every 3,000 to 10,000 years ; they could generate tall waves by creating landslides . Though local earthquakes from volcanic activity would create motion in the lake , they would likely only reach maximum magnitudes of 5.0 on the Richter scale . However , Crater Lake is poorly monitored , and not highly active seismically among the Cascade volcanoes . The largest earthquake threat originates from the Cascadia subduction zone , which could produce earthquakes with a magnitude of 8 or 9 that could lead to huge waves in Crater Lake . </P>
<P> Mazama was last active about 4,800 years ago , when an eruption took place near Wizard Island 's eastern base . This eruption took place underwater , and it produced viscous lava that created a rhyodacite lava dome , about 2,400 years after the first period of postcaldera activity . Given that Mazama has had periods of sporadic eruptions for 420,000 years , the United States Geological Survey thinks that it is `` virtually certain '' that Mazama will erupt again in the future . Mazama is considered dormant , but it remains monitored by the United States Geological Survey Cascades Volcano Observatory . Future eruptions would likely take place near the western side of the complex and within the caldera rim ; they could occur underwater . The ejection of lava rich in gas from shallow water could produce huge ash columns , but submarine eruptions at deeper depths may decrease the explosiveness of the event . Nonetheless , the rapid mixing of water and lava could produce dangerous pyroclastic surges , which are more gaseous and less solid than pyroclastic flows . Such flows could pass over topographic barriers , move rock fragments at rapid speeds of 800 feet per second ( 240 m / s ) , and travel several miles from their vent . Mazama is unlikely to produce mudflows far from the caldera , though a nearby vent outside the caldera could erupt and mix with snow . Eruptions are unlikely to produce waves that extend beyond Crater Lake , but powerful explosions could produce tall waves in the caldera . An eruption as explosive as the one 7,700 years ago is unlikely given that it would require larger volumes of magma than are known to be available within the Mazama vicinity . Moreover , landslides could flood adjacent shoreline regions , but they are not likely to induce failure of the caldera 's walls , as they rise more than 500 feet ( 150 m ) above the lake 's surface . Earthquakes from the nearby West Klamath Lake fault zone could reach magnitudes up to 7.0 on the Richter scale , but these only occur every 3,000 to 10,000 years ; they could generate tall waves by creating landslides . Though local earthquakes from volcanic activity would create motion in the lake , they would likely only reach maximum magnitudes of 5.0 on the Richter scale . However , Crater Lake is poorly monitored , and not highly active seismically among the Cascade volcanoes . The largest earthquake threat originates from the Cascadia subduction zone , which could produce earthquakes with a magnitude of 8 or 9 that could lead to huge waves in Crater Lake . </P>
when was the last time crater lake volcano erupted
when was the last time crater lake volcano erupted
about 4,800 years ago
about 4,800 years ago