|Snake River gorge cutting the|
Flood Basalt layers, through which
the Bonneville flood discharged
|Detail of the boulder field. Note preferent tilt |
of boulders towards the left, in agreement with
flow direction. More pics here and here.
|Rounded boulders left by the high waters of the|
Bonneville flood among a Neogene basalt ridge
spillway. Flood flow in the direction of the picture.
More pics here.
One thing that makes this scenario key to understand the importance of large flooding events in shaping landscape is the ubiquitous Columbia River Basalt formation (one of the largest flood basalt regions) and the Yellostone-Snake River volcanic zone. Both covered many of the areas we visited with a nearly flat layer of very fluid basalt, during the Neogene, long before the Pleistocene floods (see e.g. Fouch, Geology, 2011). The simple relief and lithological setting left by the flood basalts enhances the erosional features related to the Pleistocene water floods and the presence of vertical tectonic motions.
|Shorelines of the Catlow Pleistocene Lake (map)|
The aim is now to find the parameters and the process-based, quantitative relationships between them that determine the development of intense outburst floods in turn of a slow drainage of the lake. For this we count on a wealth of data from tens of such overtopping basins that produced such floods (see ref. by O'Connor & Beebee, 2009). In parallel, Joe Walder and Dick Iverson (USGS at Vancouver, Washington) are carrying out beautiful dam breaching experiments that add to a large body of dam failure literature. Together, this provides the behavior of overtopping basins in a very wide range of space- and time-scales.
|2012 geofieldtrip: Outburst floods along the Columbia River. (all pictures georeferenced, map here)|
Liz Safran, Jim O'connor and others are organizing a "Friends of the Pleistocene field trip" at Owyhee Canyon, Aug 23-26 where similar features will be discussed, in case you want to join.
O'Connor & Beebee (2009). Floods from natural rock-material dams Megaflooding on Earth and Mars, ed. Devon M. Burr, Paul A. Carling and Victor R. Baker. DOI: 10.1017/CBO9780511635632.008