"Cascade Range Summary"
Mount Jefferson, Oregon |
Mount Jefferson Volcano:
Mount Jefferson (3,199 meters - 10,495 feet) is a prominent feature of the landscape seen from highways east and west of the Cascades. Mount Jefferson (one of thirteen major volcanic centers in the Cascade Range) has erupted repeatedly for hundreds of thousands of years, with its last eruptive episode during the last major glaciation which culminated about 15,000 years ago. Geologic evidence shows that Mount Jefferson is capable of large explosive eruptions. The largest such eruption occurred between 35,000 and 100,000 years ago, and caused ash to fall as far away as the present-day town of Arco in southeast Idaho. Although there has not been an eruption at Mount Jefferson for some time, experience at explosive volcanoes elsewhere suggests that Mount Jefferson cannot be regarded as extinct. If Mount Jefferson erupts again, areas close to the eruptive vent will be severely affected, and even areas tens of kilometers (tens of miles) downstream along river valleys or hundreds of kilometers (hundreds of miles) downwind may be at risk. -- Walder, et.al., 1999 Eruptive History: Most of the cone (upper 1,000 meters) of Mount Jefferson is less than 100,000 years old, with much of it younger than the explosive event described above. The upper cone is composed largely of dacite lava flows and domes, many of which appear to have been emplaced when glaciers on the volcano were much large than at present. It is likely that during growth of the domes, material was shed off to form pyroclastic flows and lahars, but if so, that record has been largely removed by glacial erosion. The youngest lava flows in the Mount Jefferson area are basaltic lava flows from Forked Butte and an unnamed butte south of Bear Butte. Both of these flows postdate the large eruption of Mount Mazama (Crater Lake) of about 7,600 years. -- Walder, et.al., 1999 Localized Floods and Lahars During the last few centuries, several small lakes were formed on the flanks of Mount Jefferson when small tributary valleys becamed dammed by glacial moraines (ridges of sediment left behind by glaciers). Several of these moraines have breached during the 20th century, producing local floods and small lahars. -- Walder, et.al., 1999 MORE Mount Jefferson:
News and Current Events, Research Updates, New Reports, Hazards Assessments:
|
Return to:
[Cascade Range Volcanoes Summary Menu] ...
[Cascade Range Volcanoes and Volcanics Menu] ...
[Mount Jefferson Menu] ...
[The Volcanoes of Lewis and Clark] ...
){kind=link}
){kind=link}