Mount Hood
Credit: Public domain photo.

Mount Hood reflected in the approrpriately-named Mirror Lake in Oregon, USA.

The most recent eruptive activity was in 1865

Mount Hood is one of the Cascade Mountain Range’s active stratovolcanoes, and is located about 45 miles (72 km) east of the city of Portland, Oregon.[1] The metro area has more than 2 million residents,[2] and could potentially be in danger should this volcano have a large eruption. Also, the Columbia River is just 25 miles (40 km) to the north.[1]

The peak is 11,249 feet (3,429 meters) elevation and the volcano stands high above the surrounding terrain.[1] It was first seen by anyone who is not Native American in 1792.[3]

The mountain has Oregon’s highest elevation point,[3] and last had a major eruption in what is estimated to be 1781 or 1782.[1][3] Since then some minor eruptions have occurred, the most recent in 1865. Earthquake swarms periodically occur under the mountain, most recently in 2002. Hot springs on the slopes also indicate continuing geothermal activity.[3]

Twelve glaciers plus snow fields on the mountain are a cause for concern, because the next time the mountain erupts, dangerous lahars (flows of mud and pyroclastic material) are a certainty.[1][3]

Six ski areas exist on the mountain, and the area is a national forest. Mount Hood is also popular for hiking, and thousands climb to the summit every year. Those hiking in the winter time are advised to prepare against contracting hypothermia, one of the top causes of death over the years for those few who have perished on the mountain.[3]

In this article I use some basic volcanology terms such as crater, caldera, and stratovolcano. For anyone who would like explanations, see my InfoBarrel article on the topic.

Mount Hood seen from Portland, Oregon
Credit: Public domain photo.

Mount Hood as seen from the city of Portland, Oregon. The volcano is less than 45 miles (75 km) away.[1]

The threat Mount Hood poses to the Portland area

Avalanches and mudflows have occurred as recently as 2006. They aren’t always a result of volcanic activity, and have crossed the Columbia River and damaged bridges.[1]

Mount Hood is considered the Oregon volcano most likely to erupt next. According to USGS, the stratovolcano isn’t likely to have an enormous explosive eruption that directly threatens Portland with massive amounts of ash. They list the three main threats as being:[1]

- First, that lahars or debris flows could travel down nearby rivers and threatened nearby towns, road, and bridges and anyone in the path of these flows. These areas could also be affected by ash flows and volcanic bombs (large pieces of lava thrown into the air) in the event of an eruption.[1]

- Second, that lahars or debris flows could travel all the way into the Columbia River, causing problems at dams that serve as electricity sources.[1]

- Third, that ash spewed into the air could cause significant disruptions to air travel, affecting Portland and possibly the airport in Seattle, Washington as well.[1]

Should a large eruption occur, ash could settle down throughout the Portland area, and possibly in cities further away in the Northwestern USA,[1] which could be a significant problem. Even a few millimeters of ash can cause significant disruption to transportation systems and water systems for example, and can be very costly to clean up. Air with ash is also hazardous to breathe.[4]

Mount Hood is a very active volcano despite not having erupted for over a century. This is a short amount of time in geological terms. The volcano is closely monitored and will eventually cause problems such as those just listed, although no one knows when.[1][3]

The threat Mount Hood poses to the Portland area is not seen as being as significant as the threat posed by Mount Rainier to the north,[1] to the Seattle and Tacoma area, although unexpected things occur with volcanoes, and it could turn out that Mount Hood is the more immediate threat in the Cascades. 

Mount Rainier at sunset
Credit: From Wikipedia by Troy Mason, CC BY 2.0.

Washington's massive Mount Rainier is the largest volcano in the Cascades, and is very close to the Seattle and Tacoma metropolitan area.[5]

Other Cascades volcanoes that could pose a big problem

There are thirteen active Cascades volcanoes,[1] some of which are known to be in a much more active state than others. Despite this however, what exactly will happen in the future isn’t fully predictable, and as stated above, unexpected things can occur. Also, some pose a more obvious threat in the event of a large eruption, such as Mount Rainier and Mount Hood, due to being located near heavily populated areas.

When Oregon’s Mount Mazama (which is now Crater Lake) erupted 7,700 years ago,[6] it had such a massive eruption that only seven larger were for sure larger during the past 10,000 years.[7] Can any of the massive Cascades volcanoes produce a similar eruption? It’s not fully known.

The eruption of Mount St. Helens in 1980 was large, although what Mazama did thousands of years ago was far larger.[6] Even if we know a volcano is going to erupt, it’s not completely predictable how large an eruption will be or what exactly will happen. Scientists watching Mount St. Helens were surprised at the size of the 1980 eruption.

The point of all this is that we don’t entirely know what the future may hold, and although the science of volcanology is continuously making advancements, predicting eruptions – and also how large the will be and what exactly will happen – remains challenging,[8] although for many who study these mountains, the desire to understand how they work and how to help others who could be in harm’s way is their primary motivation.[9]