Mt. St. Helens erupted in 1980, sending out gas and pyroclastics. Geologists have found evidence of many eruptions of St. Helens, dating back 37,000 years. The mountain is huge and is composed of layers of lava and pyroclastics. Which of the following is most likely true?
It's a stratovolcano (or composite cone) - The longevity, large size, and alternating eruptions of pyroclastics and lava are classic attributes of stratovolcanoes (composite cones) that form along convergent-plate boundaries where subduction is occurring (pg 143)

Mt. St. Helens erupted in 1980, sending out gas and pyroclastic. The longevity, large size, and alternating eruptions of pyroclastic and lava are classic attributes of stratovolcanoes that form along convergent-plate boundaries where subduction is occurring.

A stratovolcano, which is often referred to as a composite volcano, is a conical volcano that has been formed from several strata of tephra and lava that have solidified over time. Contrary to shield volcanoes, stratovolcanoes are distinguished by a steep profile with a summit crater and regular intervals of effusive eruptions and explosive eruptions, however some have collapsed summit craters known as calderas.

Typically, because of its high viscosity, the lava flowing from stratovolcanoes cools and solidifies before spreading far. The worst and most economically damaging volcanic event in American history was the Mount St. Helens big eruption on May 18, 1980.

Learn more about Calderas here:

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