Earthquake activity beneath Mount St. Helens remained at a low level during June 1996. Ten earthquakes were recorded beneath the volcano during the month. None of these earthquakes exceeded magnitude 2.0. Monthly earthquake totals since January 1996 have been: January, 14; February, 13; March, 19; April, 16; May, 11; and June, 10.
During the night of June 9, a large seismic event from the
volcano triggered an automated, 24-hour alarm system. The
character of the signal suggested that the source was a rockfall
from the crater wall. This interpretation was confirmed by a
USGS crew working in the crater on June 11, who observed a large,
fresh rockfall deposit that originated from the south crater
wall. Rockfalls are a common occurrence in the crater during the
summer, and generally do not indicate any increase in volcanic
activity. Activity at the volcano remains at a safe, background
Caption: Cross-sectional view showing the locations of earthquakes beneath Mount St. Helens during June 1996. The cross-section represents a vertical slice of the crust downward from line A-A' in the map view. The earthquakes occurred in and around the magma conduit system that leads from the magma reservoir to the dome. In this graph, 0 depth is referenced to 1.5 km (about 1 mile) below the current summit of Mount St. Helens (8,363 feet above sea level). Data and graph provided by the Geophysics Program, University of Washington.
Caption: Graph showing relationship between time and depth of earthquakes beneath Mount St. Helens from July 1, 1995 to June 30, 1996. In this graph, 0 depth is referenced to 1.5 km (about 1 mile) below the current summit of Mount St. Helens (8,363 feet above sea level). Data and graph provided by the Geophysics Program, University of Washington.