During an after-meeting beer and bull session with some city staffers and a fellow city councilor the subject of natural disasters and emergency planning came up. We were glad our area was rarely on the receiving end of gigantic natural disasters such as hurricanes, tornadoes, or earthquakes (knock on wood). But we agreed that an eruption of Mt. Hood would have a long term direct impact not only on Troutdale, but on the entire region.
A large eruption of Mt. Hood would affect commerce for several weeks or months by disrupting air and shipping traffic. For instance, after the last eruptive period 200 years ago the Sandy River became filled with sediment, which drained into the Columbia River. During the 1980 Mt. St. Helens eruption, several ships were blocked upstream in the Columbia River due to the massive quantity of material flowing into the Columbia. I believe it's possible that a flow of material down the Sandy River could also damage or destroy the Sandy River, Stark Street, and I-84 bridges.
Air traffic would also be affected. Ash is a great hazard to aircraft. The fuselage, wings and engines can be severely damaged by ash. An eruption of Mt. Hood could cause flight cancellations, delays, and even in-flight emergencies. Several major air routes go directly over or near Mt. Hood. The economic impact of such a disruption would be just as significant as a disruption of water shipping.
A major eruption of Mt. Hood would also affect the Bull Run watershed, which supplies water to approximately 800,000 Oregonians. Bull Run is five miles from Mt. Hood. A volcanic eruption would contaminate the water with large quantities of sediment, which would likely cause the Portland Water Bureau to rely on its backup water source of groundwater. This could result in major losses of available water during high-demand periods. For example, during the February 1996 flood, Portland relied exclusively on groundwater for several days. During that time, elevated turbidity levels in the Bull Run reservoir did not meet federal and state drinking water standards.
An eruption of Mt. Hood could block shipping up and down the Columbia River for days or even months. The economic impact of such blockage would be devastating. According to Port of Portland statistics, the total value of waterborne imports and exports is nearly $10 billion dollars. Even a disruption of a few days would have a significant negative financial impact.
Our beer and bull session attendees all agreed that although a volcanic eruption of Mt. Hood would directly impact a large area physically, the impact due to disruption of shipping, air traffic and water supply would last far longer than the eruption itself. Our discussion had a sobering effect.