Examining a rock from a pyroclastic flow deposit, Mount Hood, OR

Above the geologist's head, a second pyroclastic-flow deposit can be seen where there is a horizontal contact (line) between the two deposits. These flows were emplaced during the Timberline eruptive period, which occurred about 1,500 years ago, and helped to build the broad fan of pyroclastic-flow and lahar deposits that forms the southwest flank of the volcano.