Final answer:
Signs of the imminent eruption of Mt. St. Helens in 1980 included increasing earthquake activity, deformation of the mountain with an outward-growing bulge, and the increasing emission of gases, indicating the upward movement of magma.
Step-by-step explanation:
The eruption of Mt. St. Helens in 1980 was signaled by a series of precursors that started being recorded by scientists several weeks before the actual event. One of the key precursors was the earthquake activity around the mountain.
From March 20th, 1980 onwards, continuous earthquake activity was noted. These tremors increased in both frequency and magnitude over a period of weeks, raising concerns about the possibility of an impending volcanic eruption.
Another significant sign was the deformation of the mountain itself. Using geodesic measurements, scientists noted that the north flank of Mt. St. Helens had begun to bulge outwards. By early May, this bulge was growing at a rate of five to eight feet per day, indicating that magma was accumulating beneath the surface.
The release of gasses was another important clue. Increases in the emission of sulfur dioxide, carbon dioxide, and other gasses were noted, signalling the upward movement of magma. Strong smell of sulfur around Mt. St. Helens also signaled that the eruption was imminent.
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