what were the aftereffects of the eruption?
An eruption column rose into the atmosphere and deposited ash in 11 U.S. states and two Canadian provinces. At the same time, snow, ice and several entire glaciers on the volcano melted, forming a series of large lahars (volcanic mudslides) that reached as far as the Columbia River, nearly to the southwest. Less severe outbursts continued into the next day
1980 eruption of Mount St. Helens
This allowed the partly molten, high-pressure gas- and steam-rich rock in the volcano to suddenly explode northwards toward Spirit Lake in a hot mix of lava and pulverized older rock, overtaking the avalanching face.

An eruption column rose into the atmosphere and deposited ash in 11 U.S. states and two Canadian provinces. At the same time, snow, ice and several entire glaciers on the volcano melted, forming a series of large lahars (volcanic mudslides) that reached as far as the Columbia River, nearly to the southwest. Less severe outbursts continued into the next day, 
where did the top of mt st helens land UNANSWERABLE
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1980 eruption of Mount St. Helens [SEP] Introduction
An earthquake at 8:32:11 a.m. PDT (UTC−7) on Sunday, May 18, 1980, caused the entire weakened north face to slide away, creating the largest landslide recorded. This allowed the partly molten, high-pressure gas- and steam-rich rock in the volcano to suddenly explode northwards toward Spirit Lake in a hot mix of lava and pulverized older rock, overtaking the avalanching face. An eruption column rose into the atmosphere and deposited ash in 11 U.S. states and two Canadian provinces. At the same time, snow, ice and several entire glaciers on the volcano melted, forming a series of large lahars (volcanic mudslides) that reached as far as the Columbia River, nearly to the southwest.