Rock Island Dam Island Pool. Rock Island Dam is constructed on Columbia River basalt similar to that which is exposed on the cliffs near the dam. These columnar basalts were formed from lava flows during the mid- to late-Miocene Epoch, some 14 to 16 million years ago. The rock is strong and durable and provides a very stable foundation for the structure. Columbia River stream flows at the Project averaged 73,700 cubic feet per second (2090 m³/s), a decrease of 37% from 2000 and 63% of the 20 year average of 116,700 cubic feet per second (3305 m³/s). The Rock Island Hydro Project
Lava bench Lava bench A lava bench is a volcanic landform with a horizontal surface raised above the level of the surrounding area. They are created when molten lava travels away from a volcanic vent and expands an old shoreline. This is the process that creates new land in the ocean that life can eventually grow on. The Hawaiian islands are an example of land that was formed this way, and the Big Island is currently still expanding due to lava benches. The Kilauea Volcano releases lava that flows down the slope of the volcano and eventually encounters the ocean; this lava