<P> There have been two United States Navy ammunition ships named for Mount Hood, despite the mountain's namesake having been an enemy commander . USS Mount Hood (AE - 11) was commissioned in July 1944 and was destroyed in November 1944 while at anchor in Manus Naval Base, Admiralty Islands . Her explosive cargo ignited, resulting in 45 confirmed dead, 327 missing and 371 injured . A second ammunition ship, AE - 29, was commissioned in May 1971 and decommissioned in August 1999 . </P> <P> The glacially eroded summit area consists of several andesitic or dacitic lava domes; Pleistocene collapses produced avalanches and lahars (rapidly moving mudflows) that traveled across the Columbia River to the north . The eroded volcano has had at least four major eruptive periods during the past 15,000 years . </P> <P> The last three eruptions at Mount Hood occurred within the past 1,800 years from vents high on the southwest flank and produced deposits that were distributed primarily to the south and west along the Sandy and Zigzag rivers . The last eruptive period took place around 220 to 170 years ago, when dacitic lava domes, pyroclastic flows and mudflows were produced without major explosive eruptions . The prominent Crater Rock just below the summit is hypothesized to be the remains of one of these now - eroded domes . This period includes the last major eruption of 1781 to 1782 with a slightly more recent episode ending shortly before the arrival of the explorers Lewis and Clark in 1805 . The latest minor eruptive event occurred in August 1907 . </P> <P> The glaciers on the mountain's upper slopes may be a source of potentially dangerous lahars when the mountain next erupts . There are vents near the summit that are known for emitting gases such as carbon dioxide and sulfur dioxide . Prior to the 1980 eruption of Mount St. Helens, the only known fatality related to volcanic activity in the Cascades occurred in 1934, when a climber suffocated in oxygen - poor air while exploring ice caves melted by fumaroles in Coalman Glacier on Mount Hood . </P>

When is the last time mt hood erupted