Scaleidoscope

Can a mountain lose height?

Can a mountain lose height?

Mount St. Helens became about 400 metres shorter in a day.

≈400 m (1,314 ft) lost on May 18, 1980

From 2,950 m before the eruption to about 2,550 m after.

Historically documented

Why this is interesting

We tend to think of a mountain's height as fixed. Mount St. Helens shows it isn't.

On May 18, 1980, the volcano's north side collapsed in one of the largest landslides in recorded history. The former summit was gone, and a large crater was left in its place.

How this measurement works

USGS gives the elevation lost during the May 18, 1980, landslide and eruption as 1,314 ft (400 m): from 9,677 ft (2,950 m) before to 8,363 ft (2,550 m) after.

The metric values are rounded, so the metre difference is best read as about 400 m. The material that disappeared from the top didn't vanish — it became an enormous debris avalanche.

See the math

Summit before
9,677 ft (2,950 m)Source value
Before May 18, 1980
Summit after
8,363 ft (2,550 m)Source value
In feet
9,677 − 8,363 = 1,314 ftCalculated
In metres
2,950 − 2,550 ≈ 400 mCalculated
Metric values are rounded
Published
≈400 m shorterResult

How certain is this?

Historically documented · before-and-after elevations from USGS. The metric figures are rounded, so the height loss is about 400 m.

Pre-eruption summit elevation was 9,677 ft; the upper part of the volcano was removed.

Sources & further reading

Follow this rabbit hole

When a mountain becomes a volume problemThe 1980 Mount St. Helens landslide was about a million Olympic pools of debris.

Keep going

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