Catastrophic Late Pleistocene Bonneville Flood, Snake River Plain, Idaho, USA

Gilbert (1890) completed a comprehensive investigation of the largest of the Pleistocene Lakes in the Great Basin of the western United States, Glacial Lake Bonneville. He found the ancient lake had a northerly outlet at Red Rock Pass that released a large amount of water; he termed the feature the “Bonneville river.” Gilbert described Lake Bonneville Flood features downstream to Pocatello, Idaho. Although other investigators worked in the area during the next 60 years, none recognized the flood features along the Snake River Plain from the Bonneville Flood.

In the mid-1950s, Harold Powers and Harold “Hal” Malde of the USGS began mapping Quaternary deposits on the western Snake River Plain. In 1960, Hal published two papers on his early interpretation of the Bonneville Flood and denoted the unique flood deposits as the “Melon gravel” formation. This led to his important contribution on the Bonneville Flood in USGS Professional Paper 596 (1968), which received GSA's Kirk Bryan Award in 1970. Hal continued mapping Quaternary deposits on the western Snake River Plain through the early 1990s (Malde, 1971, 1982, 1987, 1989a-e, and 1991). He found new and substantially higher flood deposits and erosional features on the Snake River Plain at River Mile 262, a reach conducive to detailed hydraulic modeling, which resulted in a revised Bonneville Flood discharge of about 935,000 m³/s (Jarrett and Malde, 1987). This value was 2.2 times larger than Malde's 1968 discharge estimate. Hal spent time in the field and had many communications with Jim O'Connor related to his GSA Special Paper 274 (1993) on the hydrology, hydraulics, and geomorphology of the Bonneville Flood. Malde's work led to numerous additional papers on the Bonneville Flood by other scientists. Hal's multi-decadal skilled observations and insights have had lasting contributions in geologic mapping and paleoflood hydrology to this day.