We have a couple of images of pendant bars to share. Not being geologists ourselves, we don’t want to get too deep into the topic, but we hope you will be motivated to check out the geology of the Bluff and Rocky Butte. The Rose City Bluff ground is full of river rock as we would expect given the Bluff’s origin. The Bluff is a pendant bar formed by ice age deposits from Missoula floods that flowed around Rocky Butte.
Pendant bars are large geological landforms often created by catastrophic glacial lake outburst floods. The bars are essentially elongated mounds of flood debris that form in the downstream side of obstructions, like Rocky Butte, as floodwater sweeps past. Here’s a LIDAR image of Rocky Butte and the Alameda Ridge.
These landforms are not limited to Earth. Similar pendant bars and other flood-related structures have been observed in a large outflow system on Mars, providing evidence for ancient, large-scale flooding on the planet.
“In Ares Vallis, teardrop mesas extend like pennants behind impact craters, where the raised rocky rims diverted the floods and protected the ground from erosion. Scientists estimate the floods had peak volumes many times the flow of today’s Mississippi River.
This image was taken by the Thermal Emission Imaging System instrument on NASA’s Mars Odyssey orbiter and posted in a special December 2010 set marking the occasion of Odyssey becoming the longest-working Mars spacecraft in history.” (NASA)
Rose City Bluff Restoration 