Will Mt. Hood Blow?

By Midge Pierce

Portland loves its volcanoes. On a clear day, a lucky few may catch a 10-peak view along the storied stretch from Washington to southern Oregon. The city even has the extinct Mt. Tabor in a city park.

At the top of the list here is Mt. Hood. Pilots tip their wings to it. The fit climb it. Residents revere it. Few realize that this deceptive beauty is among the nation’s most dangerous: Mt. Hood is an active volcano. It is not a question of if it will blow, but when.

Mt. Hood is one of eight very high threat volcanoes in the Pacific NW, according to Cascade Volcano Observatory seismologist Seth Moran.

“Hood has been less frequently active and less explosive than St. Helens,” he indicates. “However, people live, work and recreate much closer to Hood so even a small eruption could have a large impact.”

Hood’s most recent explosion in the 1780s lasted a decade. While considered a relatively minor event compared to blast activity dating back 30,000 years, it was enough to alter river flows and landscapes all the way to the Columbia.

When Lewis and Clark travelled along the river, they saw results of lava streams that created the Sandy River delta, which they described as full of quicksand and dead trees.

Today one is likely to see more dogs than ghost stumps in the area. Yet danger still lurks upstream where Hood occasionally billows smoke, releases gases and experiences barely detectable eruptions, loosening rocks that can cause slides and avalanches.

In addition to devastating nearby towns, Moran says a flare-up would close major east-west Highway 26 and the north-south byway 35.

The biggest worry is that eruption could come with little warning. Experts have no idea when this sleepy, though not sleeping, giant will awaken.

“No one knows exactly what to expect. Hood is not a one and done,” according to Moran.

In 1980, when remote Mt. St. Helens blew, falling ash was Portland’s major problem, but an eruption on Mt. Hood, with its semi-circle of transit routes, would cause impactful transportation and economic disruptions.

Detailing the risks, Moran told the Mt. Tabor Neighborhood Association that Hood will likely spew pyroclastic lava, melting its snowcap and glaciers, producing floods and devastating flows called lahars.

Mud and cement-like debris dense with rocks and trees could reach Government Camp, then Welches, within 30 minutes or so, gathering houses, cars and other wreckage to dump into the Columbia River.

Skiers, hikers and people living on Mt. Hood’s flanks would have little time to escape and recovery could take years.

It’s equally possible that Hood could wake-up, provide some alarming bursts and go quiet again. Even today, lava domes like Crater Rock continue to build up, break down and emit gases.

Moran says monitors are working round the clock from Portland to Hood’s Crater Rock formation to try to provide early warning.

Since a New York Times article last year indicated there were too few monitors, several more have been added for a total of 11 stations.

The moderating news is that Hood is generally not considered the Pacific NW’s greatest hazard. That honor goes to Mt. St. Helens followed by Mt. Rainier, which has far more monitoring stations than Hood.

Moran says Portland is the only major city that sits atop an active lava field that, in theory, could erupt at any time. Cinder cones could pop up anywhere  – even the airport.

Photo credit Midge Pierce

Will Mt. Hood Blow?

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