| Catastrophic flooding has eroded a discontinuous network of oversized anastomosing channels on the northwest flank of the Medicine Lake volcano. Most of these previously unrecognized channels were cut into an andesitic ash-flow tuff; boulders as large as 2 meters in intermediate diameter were moved in terrain where little rain falls today and stream erosion is nonexistent or minimal. The flooding was probably triggered by eruption of andesite tuff through a late Pleistocene ice cap on the volcano. The andesite tuff is dated at 173-143 thousand years ago. -- Donnelly-Nolan and Nolan, 1986 |
