HARTMAN MULTIMEDIA
Nature Based Multimedia Information Systems
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HARTMAN MULTIMEDIA
Nature Based Multimedia Information Systems |
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Blackhawk Landslide At the foot, of the precipitous eastern slope of
Blackhawk Mountain is one of the world's largest known landslides.
The slide extends from the mouth of Blackhawk Canyon some 8 kilometers (5
miles) to the north and has a maximum width of nearly 3.2 kilometers (2 miles),
varying in depth from 9 meters (30 feet) to 30 meters (100 feet).
It contains about ten billion cubic feet of material weighing
approximately 700 million tons. The landslide is composed of Blackhawk breccia which is
almost entirely gray, unsorted and unstratified breccia of fragments of Furnace
marble ranging in size from powder to 25 centimeters (10 inches) in diameter,
with most of the particles averaging about 2.5 centimeters (l inch) in diameter.
A small amount of other rock types occurs in the slide, including other
breccias and quartz monzonite; some of these are quite large, with one boulder
10 meters (35 feet) in its largest dimension.
The surface of the slide is typically low, rounded hills and small basins
with about 3 to 9 meters (10 - 30 feet) of local relief. A noteworthy feature is the distance that the material
slid down the gently sloping alluvial plain at the base of the mountain.
It has been hypothesized that the material rode a compressed air cushion
formed when the material was launched into the air by a gneiss ridge at the
bottom of the canyon. The speed of
the slide may have reached 272 kilometers (170 miles) per hour. Vegetation includes creosote bush scrub in the lower
elevations, and a Joshua tree woodland merging into a pinyon, Pinus
monophylla,
woodland in the higher elevations. Integrity: There
are a few inactive mines and prospects in the area, as well as jeep trails. Use: Research,
educational, observational. Some
private. Ref: Shreve,
Ronald, 1968. The Blackhawk
Landslide. Geo. Soc. of Amer. Spec. Paper 108, 47 pp. December 1976
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