Unified Interior Regions

Region 9: Columbia-Pacific Northwest

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Bulge on the north side of Mount St. Helens developed as magma push...
April 27, 1980

Bulge on the north side of Mount St. Helens developed as magma push...

A "bulge" developed on the north side of Mount St. Helens as magma pushed up within the peak. Angle and slope-distance measurements to the bulge indicated it was growing at a rate of up to five feet (1.5 meters) per day. By May 17, part of the volcano's north side had been pushed upwards and outwards over 450 feet (135 meters).

View from the northeast of a small phreatic eruption on Mount St. H...
April 10, 1980

View from NE of a small phreatic eruption on Mount St. Helens befor...

On March 20, 1980, after a quiet period of 123 years, earthquake activity once again began under Mount St. Helens volcano. Seven days later, on March 27, small phreatic (steam) explosions began.

Flyover view of Mount St. Helens prior to the catastrophic eruption.
April 10, 1980

Mount St. Helens prior to the catastrophic eruption

Mount St. Helens prior to the catastrophic eruption of May 18, 1980. Streams and lava flows also visible. View is looking southerly from oblique aerial view. Mount Hood in distance.

View looking west of Mount St. Helens' summit after several small e...
March 30, 1980

View looking west of Mount St. Helens' summit after several small e...

View looking west of Mount St. Helens' summit after several small explosive eruptions. The smaller of the two pit craters was formed first on March 27. Subsequent eruptions opened the farther crater.

Ash-covered summit of Mount St. Helens. Aerial view looking north-n...
March 30, 1980

Ash-covered summit of Mount St. Helens. Aerial view looking north-N...

Ash covered snow is a result of wind direction, resulting in left portion of cone free of ash while the right portion is covered. Snowstorms later covered these ash layers, which in turn were covered by new ash. The result was many alternating layers of snow and ash.

View from the northwest of a phreatic eruption on Mount St. Helens ...
March 30, 1980

Phreatic eruption on Mount St. Helens pre-May 18, 1981

View from the northwest of a phreatic eruption on Mount St. Helens pre- May 18, 1980 eruption.

Crater in Mount St. Helens summit, aerial view looking east....
March 27, 1980

Crater in Mount St. Helens summit and ash (swath of dark) distribut...

An east-west fault across middle of summit area and an uplift or bulge on upper north flank of the volcano are also visible in this photo.

Upper cone of Mount St. Helens before the May 18, 1980 eruption; no...
March 24, 1980

Upper cone of Mount St. Helens before the May 18, 1980 eruption; no...

Although seismic activity began under Mount St. Helens on March 20, this overflight showed no unusual features except numerous tracks of earthquake-triggered snow avalanches. No evidence of fracturing of summit area was detected during careful visual observations on the afternoon of March 24, 1980. On March 25, the first cracks were noted by Bud Kimball, Tacoma, Washington

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Summit region (Kalama age–1479 to 1720 C.E.) of Mount St. Helens lo...
September 28, 1979

Summit region (Kalama age–1479 to 1720 C.E.) of Mount St. Helens lo...

Summit region (Kalama age–1479 to 1720 C.E.) of Mount St. Helens looking northeast. Spirit Lake and Mount Adams in background. September 28, 1979.