Type Mount St. Helens, WA in the search bar in Google Earth...

Type Mount St. Helens, WA in the search bar in Google Earth and examine the crater at an eye altitude of $\sim 26,000 \mathrm{ft} .$ Based on the appearance of the crater: a. a lahar removed the north side of the volcano b. a pyroclastic eruption removed the north side of the volcano c. a lava dome grew so large that it is higher than the north side of the crater d. a glacier has eroded the north side of the crater

Type Mount St. Helens, WA in the search bar in Google Earth and examine the crater at an eye altitude of $\sim 26,000 \mathrm{ft} .$ Based on the appearance of the crater:
a. a lahar removed the north side of the volcano
b. a pyroclastic eruption removed the north side of the volcano
c. a lava dome grew so large that it is higher than the north side of the crater
d. a glacier has eroded the north side of the crater

Key Concepts

Pyroclastic Eruptions

Pyroclastic eruptions involve the explosive fragmentation of magma, producing hot gas, ash, and fragmented rock that can be forcefully ejected from a volcano. These events are capable of rapidly reshaping the structure of a volcano, including the removal or alteration of parts of the crater, due to the high-energy dynamics involved.

Lahars

Lahars are volcanic mudflows composed of water mixed with volcanic debris, often triggered by intense rainfall or melting snow and ice during or after an eruption. They are capable of eroding and reshaping the landscape around a volcano, although their erosional effects typically differ in appearance from those produced by explosive eruptions.

Lava Domes

Lava domes are formed by the slow extrusion of viscous lava near a volcano's vent. Over time, the accumulation of this viscous material can create a rounded, steep-sided mound that may alter the pre-existing morphology of a volcanic crater. Lava domes generally grow gradually and change the topography rather than the abrupt removal of pre-existing features.

Glacial Erosion

Glacial erosion occurs when glaciers move over the landscape, carving and sculpting the underlying rock through processes of plucking and abrasion. This type of erosion can significantly modify the shape of a volcano’s flanks and crater, but its effects are typically characterized by broad, smooth, sculpted surfaces rather than the concentrated removal seen with explosive eruptions.

Volcanic Crater Morphology

Volcanic crater morphology refers to the structure and features of the crater formed by various volcanic processes such as explosive eruptions, lava dome growth, and erosional phenomena. Understanding the morphology of a crater involves analyzing its shape, asymmetries, and any signs of selective removal or deposition, which can indicate the dominant volcanic or erosional processes that have influenced its formation.

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