Glacier Outburst Floods at Mount Rainier, Washington State, U.S.A.

Abstract

During the twentieth century, glacial outburst floods have been the most destructive natural events on Mount Rainier, a stratovolcano in the Cascade Range in Washington State, U.S.A. In the period between 1930 and 1980 numerous floods were reported from five glaciers on the mountain, most of which flowed from Nisqually, Kautz, or South Tahoma Glaciers on its southern flank. Such floods threaten lives and property because they occur without warning and quickly mobilize the loose volcanic debris into debris flows.A monitoring program was begun in 1987 which was designed to measure the dimensions and timing of outburst floods, but this has been unsuccessful because no floods have yet occurred on the monitored streams. Four floods did burst from South Tahoma Glacier that was unmonitored, but in spite of this they have been useful in providing evidence of flood storage and release mechanisms. All flood volumes were found to be of approximately similar orders of magnitude, of 1 × 105 m3 of water, indicating that all floods probably had similar mechanisms for storage and release of water. Hydraulic pressure considerations indicate that such a large volume of flood water would be stored at the bed of the glacier rather than in isolated englacial cavities. The stepped bedrock terrain provides an ideal setting for the formation of subglacial cavities capable of storing the volumes of flood water noted.

Frequent outburst floods from South Tahoma Glacier, Mount Rainier, U.S.A.: relation to debris flows, meteorological origin and implications for subglacial hydrology

“…All outburst floods from South Tahoma Glacier since 1967 have occurred during either summer or early autumn, as noted also by Driedger and Fountain (1989) and Scott and others (1992). We did statistical analysis of meteorological data collected near South Tahoma Glacier to test whether outburst Hoods have been correlated with atypical weather conditions, and whether meteorological data might be useful predictors of outburst-flood occurrence.…”

“…Washington, the highest volcano in the coterminous United States. The smallest, but most frequent, of these debris Hows have generally been considered to originate as glacial outburst floods (Richardson, 1968; Crandell, 1971: Driedger and Fountain, 1989; Scott and others, 1992). Transformation from water Hood to debris flow generally occurs in channels cut into stagnant ice and glacially derived sediment near glacier termini.…”

Water flow through temperate glaciers

“…The differences in material properties of the dams and in erosion mechanisms are evidently less important than the flow hydraulics, which are the same in both cases. Another class of outburst floods involves the abrupt release of water from subglacial or englacial storage [Haeberli, 1983;Driedger and Fountain, 1989]. Outburst floods of this type, which are by their nature unanticipated and poorly described, seem to be triggered by rapid input of rain or meltwater to the glacier.…”

“…From (14) we estimate an upper bound for QMAX of ---100 m3/s. Flood peaks of this magnitude can be extremely destructive in small alpine drainage basins, particularly if the water floods transform to debris flows [Driedger and Fountain, 1989;Walder and Driedger, 1995].…”

Hydraulic modeling of glacial dam‐break floods on the West Branch of the Susquehanna River, Pennsylvania

“…Current glaciation can lead to the creation of megafloods (jökulhlaups) in some regions of the world, which enable investigation of water flow through glaciers and provide supplementary information for simulating paleofloods. For example, the mechanisms of the generation of modern glacial outburst floods and the estimation of the flood magnitude have been covered by Driedger and Fountain [1989], Mayo [1989], Motyka and Truffer [2007], and Hewitt and Liu [2010]. Fountain and Walder [1998] summarize the general flow of water through temperate glaciers, including a description of potential glacial outburst flood initiation mechanisms.…”