Images

Oblique aerial view of San Andreas Fault (between white arrows) in southeastern Coachella Valley, near Red Canyon; view to the west.

The Mameyes, Puerto Rico, landslide, 1985. This landslide destroyed 120 houses and killed at least 129 people. The catastrophic slide was triggered by a tropical storm that produced extremely heavy rainfall.

Aerial view of Armero destroyed by lahars from Nevado del Ruiz volcano, Colombia, on November 13, 1985.

Lava fountain heights at Pu‘u ‘Ō‘ō reached a maximum of 295 m (970 ft) around the time this photo was taken during episode 38.

Three Sisters volcanoes (left to right - South, Middle, and North) viewed from the south, Oregon. Foreground rhyolite Newberry flow is one of most recent eruptive units (2.2 ka).

The lava dome was taller than a 66-story building and almost as wide as the length of nine football fields. The dome completely fills the camera's field of view. Compare with image taken August 22, 1981 from the same location with the same camera.

Hydrologists measuring stream discharge and took water samples to determine how much sediment is suspended in the stream and how much sediment is moving along the streambed.

Aerial view, from the east, of waning lava fountain from Pu'u 'O'o on Hawai'i Island's Kilauea Volcano. Taken at the end of eruption episode 32. Pu'u 'O'o rose 209 meters above the pre-1983 surface (928 meters above sea level).

Gas Plume during the 1985 eruption of Kīlauea, Hawaii blocks out the sun. This image was taken from Kīlauea summit during episode 32 of the Pu‘u ‘Ō‘ō eruption on the middle East Rift Zone of Kīlauea. USGS image by J.D. Griggs on April 22, 1985.

USGS Hawaiian Volcano Observatory scientists monitor Mauna Loa, the largest active volcano on Earth. In this 1985 aerial photo, Mauna Loa looms above Kīlauea Volcano’s summit caldera (left center) and nearly obscures Hualālai in the far distance (upper right).

Mount Jefferson in Oregon seen from the east.

Belknap Shield Volcano viewed from McKenzie Pass, Oregon. Photo by Lyn Topinka.

Mount Washington peak in central Oregon.

Mount St. Helens four years after the May 18, 1980 eruption—lava dome in the crater and drainage channels development on flanks; view from Johnston Ridge.

Lava fragments ejected by lava fountains are called tephra, a general term for all fragments, regardless of size, that are blasted into the air by explosive activity. A variety of terms are also used to describe specific types of fragments, including Pele's hair, Pele's tears, scoria, spatter, bombs, and reticulite.

Low fountains in foreground erupting from a fissure that opened just before the main vent began to erupt.

Lava dome within Mount St. Helens crater grew between 1980 and 1986 as dacitic lava erupted from the vent. This photograph, taken in September 1984.

Vegetation began reappearing as early as the summer of 1980 as many small trees and plants were protected by the snowpack on May 18. Seeds, carried by the wind or by animals, also entered the area and grew. By 1985, the ridges surrounding the volcano were covered with new growth.

The strength of the magnetic field increased as the dome cooled and magnetic minerals formed. During the eruptions the strength usually changed rapidly as magma heated and deformed the dome.

An increase in deformation rates is an indication that magma is slowly entering the dome. In the early 1980s deformation rates often reached 30 feet per hour (10 meters/hour) as magma rose and the dome expanded before extrusion started. During the winter months, the instrument stations often had to be dug out of the snow before measurements could be made.

The U.S. Geological Survey established both periodic and continuous 24-hour monitoring programs at Mount St. Helens to study and predict eruptions. In this slide, geologists used a steel tape to measure the distance across a crack on the crater floor. Widening of cracks was an indication that magma was rising and deforming the area, leading to an eruption.