International Glaciospeleological Survey
The beginning of a New Glacier Forming in the Crater of Mount St. Helens.
Snow Accumulation in the Crater of Mount St. Helens.
Charles H. Anderson Jr and DR. Mark Vining International Glaciospeleological Survey (IGS)© "IGS Crater Team Scientists "
Dec. 15, 2000
INTRODUCTION
The association of the International Glaciospeleology Survey has studied the glaciokarstic phenomenon in many glaciers of the world, from Washington State, Canada, Alaska etc. A new forming glacier in the Crater of Mount St. Helens has obtained the most exciting results, on both the exploration and scientific research fronts.
On Mount St. Helens, we have had a unique opportunity to study the interaction of geothermal energy with the accumulation of alpine snowpack from its inception after a major eruption. We began investigative work in the crater in 1981 (Anderson and others,2000). Yearly surveys began in 1982 with mapping, description, and photography of cave passages, snow, firn, and ice. This investigation involved reconnaissance mapping and sampling from 1981 through 2000 by members of the International Glaciospeleological Survey (IGS) with the permission of the U.S. Forest Service and Mount St. Helens National Volcanic Monument.
Over the last 20 years snow, ice and rock debris have average in excess of 325 feet thick have and in places there are 450 to 600 feet deep, that have accumulated behind the lava dome. A new glacier is now forming in the crater of Mount St. Helens. A permanent body of ice has accumulated in the crater. IGS Crater Team Scientists FIND THE START OF A NEW GLACIER crater Leader Charles H. Anderson Jr. in 1999.
Figure 1. View into the crater from the north in the summer of 1998. Firn reaches around both sides of the Lava Dome and the active glacier front. We physically confirmed this by digging to and observing the solid ice mass in several places. The active moving ice under the rock debris on the east side of the dome. The glacier front on the west is beneath a veneer of rock debris.
CRATER SNOW FIRN AND GLACIER ICE
The shade of the steep crater walls to the east, south, and west largely protects the accumulation. It is not readily apparent from a distance that glacier ice is present in the crater, but bergschrunds and crevasses can be seen around the crater walls where snow and rockfall debris collect continually. The crater ice body is an incipient glacier that continues to grow. It is not readily apparent from a distance that glacier ice is present in the crater, but small bodies of ice on the south crater wall behind the Lava Dome have crevasses and flow features, indicating their transformation into glaciers. The snows stacking higher each year have locally compressed the lower layers into dense, crystalline glacier ice. The ice body shows signs of flow around both sides of the Lava Dome and is flowing out toward the north side of the dome.
The snows stacking higher each year have locally compressed the lower layers into dense, crystalline glacier ice. The ice body shows signs of flow around both sides of the Lava Dome and is flowing out toward the north side of the dome. Because of the severely limited quantity of ice density data, the mean ice density and therefore the total mass of ice can only be estimated. The ice density at the base of the crevasses and parts of the glacier front has been measured at 0.85 g/cc and above, corresponding to solid glacier.
Ice And Snow Volume 2000
Photo By USGS. In the winter and early spring, snow tumbles down avalanche chutes on the crater walls. Notes cave entrance in front of picture.
CRATER SNOW, FIRN, AND ICE
A growing body of firn, ice and glacier mixed with rock debris, which we call the ‘crater ice body’, has accumulated in the crater of Mount St. Helens since 1982 through 2000. The shade of the steep crater walls to the east, south, and west protects this accumulation. The crater headwall rises to 2550 m (8365 ft) on the south. The contiguous crater floor ice body extends from a maximum elevation of 2000 m (6560 ft) south of the Lava Dome, downward to the northeast and north around both sides of the dome. The crater floor north of the dome (1800 m or 5900 ft in elevation) hosts only seasonal snow accumulations.
Cave Description
We mapped the Mount St. Helens caves by compass and steel tape survey. All gear was carried on foot. We recorded our observations on the surface and inside the caves with videotape and still camera. We visually estimated the physical dimensions of rooms and cave features.
We found 20 entrances to the caves and mapped these are the entrances of caves as of Oct. 2000. around the perimeter of the Lava Dome during the period from 1996 through 2000. Some have spectacular large rooms. Most have small rooms and crawlways. Cave features include scalloped ceilings and walls, Moulin’s in the ceiling, multiple domes connected by crawlways, and skylights. In winter, short-lived ice stalactites, stalagmites, and helictites form inside the caves from water dripping from protrusions on the cave ceiling. Cave floors are formed by the crater floor and, in places, the dome flanks. Room sizes range from 4.6 by 4.6 by 2.4 m (15 by 15 by 8 ft) high to 12 by 24 by 6 m (40 by 80 by 20 ft) high. Most caves occur in the presence of fumaroles. Other caves form adjacent to the dome where melt water undermines the ice body.
CRATER ICE CAVES
The crater floor has been progressively covered by a layer of snow, firn, and glacier ice since as early as 1986. Heat, steam, and volcanic gases from the crater fumaroles have melted over 2,415 m (7925 ft) of cave passage in the crater ice mass. The caves are in approximate balance with the present geothermal heat release. Geothermal activity influences the dimensions, location, ceiling, wall, and wall ablation features of these caves. Cave passages are located above fumaroles and fractures in and adjacent to the dacite dome. Cave passages gradually enlarge by ablation, caused by outside air circulation and by geothermal sources beneath the ice. The passages form a circumferential pattern around the dome, with entrance passages on the dome flanks.
Crevasse 2000 Lava Dome, snow, Ice and Glacier in the Crater 2000
Photos By Charles Anderson Jr.
Photos By Charles H. Anderson Jr.
Descending passages have vertical sides and ceilings that are convex upward. Passages paralleling the slope contours are often shaped like right triangles with the 90-degree angle located at the junction of the downslope ice wall and the ice ceiling. Floors are composed of mud with up to boulder-size volcanic rubble and slope about 30 degrees. Against the Lava Dome flanks, the slope may exceed 40 degrees.
Photos By Charles H. Anderson Jr., Sept. 2000
We have observed an active glacier snout at the northwest base of the lava dome. This glacier is almost entirely covered by rock debris, and is not readily apparent to casual view. A substantial stream can be seenissuing from the glacier at the marked glacier cave. It re-enters firn nearly at the same point and disappears into the unconsolidated crater detritus under the firn field north of the dome.
Map of Crater 1998
REFERENCES CITED
Anderson, C. H., Jr.; Dr. Mark Vining, v. 27, 10 p. Observations of Glacial, Geomorphic, Biologic, and Mineralogic Developments in the Crater of Mount St. Helens, Washington, Dec. 1999, Washington Geology
Anderson, C. H., Jr.; Behrens, C. J.; Floyd, G. A.; Vining, M. R., 1998, Crater firn caves of Mount St. Helens, Washington: Journal of Cave and Karst Studies, v. 60, p. 44-50.
Anderson, C. H., Jr.; Vining, M. R., 1997, Progress report on crater environment development, Mount St. Helens, Washington: presented to Mount St. Helens National Volcanic Monument, International Glaciospeleological Survey, Seattle, Washington, 16 p.
Anderson, C. H., Jr.; Vining, M. R.; Nichols, C. M., 1994, Evolution of the Paradise/Stevens glacier ice caves: Journal of Cave and Karst Studies, v. 56, p. 70-81.
Anderson, C. H.; Halliday, W. R., 1969, The Paradise ice caves, Washington-An extensive glacier cave system: National Speleological Society Bulletin, v. 31, p. 55-72.
Halliday, W. R.; Anderson, C. H., Jr., 1970, Glacier caves: Studies in Speleology, v. 2, pt. 2, p. 53-59.
Kiver, E. P.; Mumma, M. D., 1975, Mount Baker firn caves, Washington: The Explorers Journal, p. 84-87.
Kiver, E. P.; Steel, W. K., 1975, Firn Caves in the volcanic craters of Mount Rainier, Washington: Journal of Cave and Karst Studies, v. 37, p. 45-55.
Le Guern, F.; Ponzevera, E.; Lokey, W.; Schroedel, R. D., 1999, Mt. Rainier summit caves volcanic activity [abstract]. In Northwest Scientific Association, A century of resource stewardship and beyond-Mount Rainier National Park 100th Anniversary Symposium: Northwest Scientific Association, p. 40.
Mills, H. H., 1992, Post-eruption erosion and deposition in the 1980 crater of Mount St. Helens, Washington, determined from digital maps: Earth Surface Processes and Landforms, v. 17, p. 739-754.
Mills, H. H.; Keating, G. N., 1993, Maps showing posteruption erosion, deposition, and dome growth in Mount St. Helens crater, Washington, determined by a geographic information system: U.S. Geological Survey Miscellaneous Investigation Series, unpaginated.
Glossary
crevasse - a deep, nearly vertical fissure formed by glacier movement over an uneven surface. A crevasse is conclusive evidence that plastic deformation is taking place in glacier ice.
firn- a material that is transitional between snow and ice, being older and denser than snow but not yet transformed into glacier ice. Snow becomes firn after existing through one summer melt season; firn becomes glacier ice when its permeability to liquid water drops to zero.
glacier ice - a naturally accumulated ice that has reached a bulk density in excess of 0.82 g/cc. It possesses an intergrown crystalline matrix and flows plastically under its own weight.
ice, ice body - an accumulated body of firn and ice in the Mount St. Helens crater, regardless of its density, texture, or fraction of non-ice content (air and rock debris).
rock debris - rock fragments that have fallen from the crater walls after the eruption.
crawlway - a cave passage that can be navigated only by crawling.
moulin- a circular, nearly vertical hole or shaft in the ice of a glacier, formed by percolating surface water and enhanced by air circulation.
skylight- an opening to outside light in the ceiling of a cave.
stalactite - a cylindrical or conical dripstone deposit that hangs from the ceiling of a cave.
stalagmite- a cylindrical or conical dripstone deposit that rises from the floor of a cave.
cave pearl - an unattached, subspherical to spherical calcite concretion formed in splashing or dripping water, usually deposited on a sand particle or rock fragment nucleus.
dripstone, flowstone - mineral coatings (usually calcite, but may be other minerals or ice) deposited by precipitation from water flowing over an exposed surface, usually but not only found in caves. The distinction indicates the nature of water flow during growth: dripstone forms free-hanging or free-standing deposits; flowstone forms as a wall or floor coating.
helictite - a curved, angular, or dendritic twig-like growth from a flowstone or dripstone surface.
travertine, tufa - a dense, finely crystalline massive or concretionary limestone of white, tan, or cream color, commonly having a fibrous or concentric structure and splintery fracture; formed by rapid chemical precipitation of calcium carbonate from solution in surface or ground water, as by agitation of stream water or by evaporation. The spongy or less compact variety is called tufa.
