What kind of phenomena resulted in the Crater Lake eruption?

Question

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Answer 1

Subduction of the Juan de Fuca plate beneith North America (which forms the Cascades).

Answer 2

The Crater Lake volcanic basin was created when the 12,000 foot (3,660 meter) high Mount Mazama collapsed 7,700 years ago following a large eruption.

Volcanoes are a natural way that the Earth and other planets have of cooling off. Planets are warm in their mantles. Heat inside planets escapes towards their surfaces. For reasons that are not well understood, heat sometimes melts rocks, which then rise bouyantly toward the planet's surface. When the hot rocks - called magma - and included gases break through the crust, an eruption occurs. The buildup of ash and lava flows around the eruption hole (or vent) makes a volcano. Some volcanoes erupt for only a short time - a few days to weeks and never erupt again.

Volcanoes are generally found where two to three tectonic plates pull apart or are coming together. A mid-oceanic ridge, like the Mid-Atlantic Ridge, has examples of volcanoes caused by "divergent tectonic plates" pulling apart; the Pacific Ring of Fire has examples of volcanoes caused by "convergent tectonic plates" coming together. By contrast, volcanoes are usually not created where two tectonic plates slide past one another (like the San Andreas fault). Volcanoes can also form where there is stretching of the Earth's crust and where the crust grows thin (called "non-hotspot intraplate volcanism"), such as in the African Rift Valley or the European Rhine Graben with its Eifel volcanoes).

Finally, volcanoes can be caused by "mantle plumes," so-called "hotspots;" these hotspots can occur far from plate boundaries, such as the Hawaiian Islands.

Answer 3

From Crater Lake Data Clearinghouse:

"Crater Lake partially fills a type of volcanic depression called a caldera that formed by the collapse of a 3,700 m (12,000 ft) volcano known as Mount Mazama during an enormous eruption approximately 7,700 years ago. "

Check the link for the full geologic history of Crater Lake.