Dante II

The Mission

The Mountain

Mount Spurr, Alaska

       Mt. Spurr             Crater Peak          East Ridge         Descent Route

The Mt. Spurr volcano

Mt. Spurr is part of the Aleutian volcano arc which extends about 1,550 miles along the southern edge of the Bering Sea and Alaskan mainland. This classic arc contains some 80 Quaternary period statovolcanoes and calderas.

Aleutian arc volcanism is the result of active subduction of the Pacific Plate beneath the North American Plate. The 5,400-mile-long Aleutian trench that extends from the northern end of the Kamchatka trench to the Gulf of Alaska marks the boundary between the two plates.

The Spurr volcanic complex consists of an ancestral volcano whose growth was terminated by the formation of an avalanche caldera. The present Mt. Spurr then grew in the center of the caldera and the active Crater Peak grew in the breach. On June 27, 1992 the Crater Peak vent awoke again after 39 years of dormancy and burst into eruption after 10 months of elevated seismic activity. Two more eruptions that year occured in August and September.

The actual active volcanic vent of Mt. Spurr is located in Crater Peak, which is, as described earlier by one team member after first viewing the volcano, "a wart on the side of a larger mountain". Crater Peak (7575 feet) is located on the southern slope of Mt. Spurr (11070 feet) and the crater itself is shaped approximately like an 700-foot diameter open funnel. The north and west walls of the crater rise almost vertically 1000 feet from the crater floor, and are topped by a 100 foot thick layer of glacial ice coming down from the upper slopes of the mountain. Due to a combination of the relative youth of these rock faces (which were first exposed in the 1992 eruption of the volcano) and material being pushed into the crater by the glacial flow, there is almost constant rock fall from these walls. Material ranging in size from pebbles to 6-foot diameter boulders crash down from the heights of the walls every minute or two. Snow melt from the ice and recent snow storms runs down the walls in thin waterfalls, much of which is apparently turned to steam when it reaches the fumeroles at the bottom of the crater. As a result the crater is constantly alive with sound, with the waterfalls and hissing steam forming a background of white noise punctuated by loud crashes as free-falling boulders slap the cliff faces.

The southern wall slopes up at angles between 30 to 70 degrees for about 500 feet from the bottom of the crater. The portion which would rise above that level was blown out of the mountain by the 1992 eruption, leaving a relatively flat snow-covered plateau nearly 200 feet wide between the crater and the exterior mountainside. Under the snow, the plateau is covered in several feet of thick, gooey black mud made from the volcanic ash of the eruption which sticks tenaciously to everything. As with the other faces of the crater, the exposed rock of the south wall varies from a mottled gray to a deep red in color (presumably due to a high iron content in some layers of the rock).

The east wall slopes up from the southern edge to blend in with the north wall. It is at the edge of the southern plateau between the south and east walls that Dante has been placed to begin it's walk to the crater floor. "Crater floor" is a term that is applied to a somewhat nebulous area at the bottom of the crater which includes the talus piles built up from the rock fall off the north and west walls, the exposed fumerole fields which are primarily along the south- eastern wall, the boulder fields above the fumeroles, and an unknown area in the center of the crater which is constantly hidden by the steam and gases emitted from the fumeroles.

It is intended that the robot will walk down the south-eastern wall and through the boulder fields at least as far as the upper edges of the fumerole fields to gather readings from the gas sensors on board, and to view behind a large rock bulge to investigate an area hidden from view from the crater rim. Depending on an examination of the local terrain in the fumerole fields and the time required to traverse the boulder field, further exploration into the fumerole field toward the unknown area may be considered.

Facts about Mt. Spurr that influenced the Dante II design