Blue Lake Crater

Blue Lake Crater is a maar, or a broad, low-relief volcanic crater, in the U.S. state of Oregon. Located in Jefferson County, it consists of three overlapping craters, which hold Blue Lake. The drainage basin for Blue Lake has very steep, forested slopes and is mostly part of the explosion crater left by the volcano's eruption. The volcano lies within the Metolius River basin, which supports a wide array of plant life, large and small mammals, and more than 80 bird species. In 2009, Governor of Oregon Ted Kulongoski signed a bill designating the Metolius River basin as an area of critical concern, preventing large-scale development on the land and protecting its wildlife.

Despite having erupted at some point within the past 4,000 years, Blue Lake Crater is considered one of the least-known Holocene volcanoes in the Cascade volcanic arc. It forms a modest volcanic cone, its lake surrounded by a crescent-shaped, agglutinate ridge consisting of volcanic bombs. The northern side of Blue Lake Crater's rim collapsed during eruptive activity, while the southern wall remains intact. The overall composition is mafic , chiefly basalt and picrite basalt . Other associated volcanic features include a chain of spatter cones about 3.7 miles to the south, which erupted material that shares petrographic qualities with erupted material from Blue Lake Crater. Geologists disagree on the exact date of Blue Lake Crater's most recent activity; W. E. Scott and E. M. Taylor place the eruption at 3,440 ± 250 years ago, while more recent publications estimate that date as the maximum age and suggest it is more likely the eruption occurred about 1,330 ± 140 years ago. The United States Geological Survey has assessed the threat potential from Blue Lake Crater as "Low/Very Low."

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