On Christmas Day , an intense rainstorm rapidly melted snow and triggered a small landslide in fragmental debris in upper Polallie Creek. The resulting lahar moved downvalley at 25 to 35 miles per hour. At the mouth of Polallie Creek, the lahar spread out, killing a camper and temporarily damming the East Fork Hood River. Small lahars such as this occur every few years at Mount Hood, but few have been as destructive. Two past eruptions at Mount Hood provide perspective on the impact of future large events.
Both were associated with eruptive activity that triggered debris avalanches and were accompanied by lava extrusion, pyroclastic flows, and lahars.
One represents a truly catastrophic event. About , years ago, a large portion of the volcano's north flank and summit collapsed. The resulting debris avalanche transformed into a lahar that swept down the Hood River valley. At the river's mouth, where the town of Hood River now stands, the lahar was feet deep. Since that time lava has filled in the scar left by the debris avalanche. On the south side of the volcano, the scar from a 1,year-old debris avalanche is still visible, forming the amphitheater around Crater Rock.
A lahar formed by this event traveled the length of the Sandy River valley, depositing boulders as large as 8 feet in diameter, 30 feet above present river level where the towns of Wemme and Wildwood now stand. The lahar spread out over the delta at the mouth of the Sandy River and pushed the Columbia River to the north. This event, although large by Mount Hood's standards, was only about one-tenth the size of the ,year-old event.
Mount Hood's next eruption is much more likely to be smaller than or similar in size to the 1,year-old event. An eruption similar in size to the ,year-old event, although possible, is much less likely. Today Mount Hood shows no signs of imminent volcanic activity, but hot steam vents, or fumaroles, near Crater Rock attest to heat below. On clear, cold, windless days, a steam plume is often seen rising from the fumaroles.
Visitors to Mount Hood frequently smell the "rotten egg" odor of the fumarole gas, whose composition indicates that magma lies a few miles below the summit. Scientists expect the next eruption to consist of small explosions and the growth and collapse of lava domes, generating pyroclastic flows, ash clouds, and lahars.
Lahars pose the greatest hazard because more people live downstream in lahar-prone river valleys than live on the volcano's flanks. Thus, it is important to know where one lives, works, and plays in relation to Mount Hood's hazard zones. Hazard zones shown on the map were determined on the basis of distance from the volcano, vent location, and type of hazardous events.
Proximal hazard zones P are areas subject to rapidly moving debris avalanches, pyroclastic flows, and lahars that can reach the hazard boundary in less than 30 minutes, as well as to slow-moving lava flows.
Areas within proximal hazard zones should be evacuated before an eruption begins, because there is little time to get people out of harm's way once an eruption starts. Most pyroclastic flows, lava flows, and debris avalanches will stop within the proximal hazard zone, but lahars can travel much farther.
Distal hazard zones D are areas adjacent to rivers that are pathways for lahars. Estimated travel time for lahars to reach these zones is more than 30 minutes, which may allow individuals time to move to higher ground and greater safety if given warning.
Photos of Dallol Look at one of the most surreal landscapes on Earth, created by hot springs, colorful salt deposits and volcanic gas vents.
Get the ad-free version! Why is there advertising on this site? Support us - Help us upgrade our services! Copyrights: VolcanoDiscovery and other sources as noted. Use of material: Most texts and images, in particular photographs, on this website are protected by copyright. Further reproduction and use of without authorization is usually not consented. Over the ensuing millennia, further eruptions continued to shape and give rise to the mountain.
At its highest, Mount Hood topped 12, feet, with ice and erosion reducing the peak to its current height. Eruptions on Mount Hood have been characterized less by powerful explosions than by the gradual building and collapse of lava domes, pyroclastic flows, and volcanic mudflows known as lahars. In the past 2, years, Mount Hood has experienced three eruptive periods: the Timberline period, just over 1, years ago; the Zigzag period, about years ago; and the Old Maid period, between the s and the early s.
Although the mountain has not erupted since then, vents on its upper reaches, called fumaroles, still emit sulfurous steam, and minor earthquakes occur frequently deep beneath the mountain. A twelfth glacier, christened the Salmon Glacier in and later renamed the Palmer Glacier, lost enough of its volume and mobility over the twentieth century to be widely regarded as a snowfield. The mountain is also the source of five major rivers—Salmon, Zigzag, Sandy, Hood, and White—and is the centerpiece of the Mount Hood National Forest, a million-acre forest that more than four million people visit each year.
The glaciers are not the source of drinking water for the City of Portland, which gets its water from the Bull Run Watershed, a square-mile protected watershed in the Mount Hood National Forest northwest of Mount Hood proper. Bull Run is separated from the mountain by a prominent ridge and is fed largely by rainfall, which ranges from inches a year at lower elevations to inches higher up.
Meltwater from the Eliot, Coe, and Newton Clark glaciers feeds the three streams that eventually form the Hood River, which farmers and orchardists use to irrigate crops and fruit trees in the Hood River Valley. The Mount Hood National Forest contains no fewer than fifteen municipal watersheds. The mountain and its surrounds are home to a diversity of wildlife, including black-tailed deer Odocoileus hemionus , elk Cervus elaphus , coyotes Canis latrans , yellow-bellied marmots Marmota flaviventris , black bears Ursus americanus , mountain lions Puma concolor , and many other species common to the Northwest.
Bald eagles Halioaeetus leucocephalus , ospreys Pandion haliaetus , northern spotted owls Strix occidentalis caurina , American dippers Cinclus mexicanus , gray jays Perisoreus Canadensis , downy woodpeckers Picoides pubescens , and rufous hummingbirds Selasphorus rufus also live on and around the mountain.
Botanical species include ferns e. Tree species include Douglas-fir Pseudotsuga menziesii , western red cedar Thuja plicata , noble fir Abies procera , ponderosa pine Pinus ponderosa on the eastern side of the mountain, western hemlock Cicuta Douglasii , bigleaf maple Acer macrophyllum , vine maple Acer circinatum , black cottonwood Populus trichcarpa , and the rare whitebark pine Pinus albicaulis.
For thousands of years, Native people lived in the shadow of Mount Hood, primarily along the Columbia River and its tributaries and in the Willamette Valley. Middle and Upper Chinookan tribes and bands, including the Cascades and Molala people, lived in the Cascade Range and had a north-south trail system that approximates the modern-day Pacific Crest Trail.
They hunted and fished around Mount Hood; gathered huckleberries, roots, and edible plants; and harvested plants such as beargrass for use in basket weaving. Native people regarded the mountain as a sacred place. The mountain and the lands surrounding it were ceded to the United States through the Kalapuya Treaty of and the Treaty with the Tribes of Middle Oregon, which was ratified in The first recorded sighting of the mountain by Europeans was in While leading a small expedition of two longboats up the Columbia River in October , Lt.
William Broughton, a British naval officer, described the mountain and named it in honor of Lord Samuel Hood, a British admiral who never saw the mountain. The Lewis and Clark Expedition also saw the mountain in Mount Hood was a major landmark for early settlers who came to Oregon on the Oregon Trail.
In late summer , Samuel Barlow set off with a wagon train from The Dalles in search of a land route around Mount Hood. The next year, Barlow developed the route known as the Barlow Road , which many settlers used to make their way to the Willamette Valley. Small communities were established on the mountain over the decades, including Zigzag, Rhododendron, Government Camp, and Parkdale. Multimedia Gallery. Park Passes. Technical Announcements. Employees in the News. Emergency Management. Survey Manual.
The shadow of the summit of Mount Hood, Oregon on a morning cloud bank. Illumination Rock in the foreground. Credit: Howle, James F. Public domain. Mount Hood, which has been active for at least , years, occupies a long-lived focus of volcanic activity that has produced ancestral Hood-like volcanoes for the past 1.
Much of the Mount Hood edifice is formed of lava flows, but eruptive activity during the past 30, years has been dominated by growth and collapse of near-summit lava domes to produce broad fans of pyroclastic flow deposits. Similar deposits were probably formed in Mount Hood's past but were largely eroded, especially during ice ages, and are poorly represented in the geologic record.
The last two periods of eruptive activity occurred about 1, years ago and in the late 18th century. In addition to Mount Hood, other volcanoes scattered through the nearby area have erupted during the past , years.
In contrast to the long-lived activity at Hood, each of these regional volcanoes was active for a relatively short period of time.
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