Is Seattle Ready to Deal With Volcano Ash and Lahars?

Thursday, October 16, 2014, by Curbed Staff

Go ahead, name the volcanoes.

They top the eastern skyline. Everyone knows Rainier. Skiers are very aware of Baker. St. Helens made itself obvious in 1980. Adams is frequently forgotten, even though it is the second highest. And Glacier Peak is barely known, rarely seen and so isolated it doesn't have a visitors center. They're more than just pretty mountains. They have a tendency to blow up. That's more than a show, and as 1980 residents can tell you, the ash and mud will flow.

Mt. St. Helens' eruption is history. It was more than 30 years ago, so most people treat it as a done deal. The ash closed I-90 for ten days. Airline flights were cancelled. The air filters in cars and trucks clogged, which meant having a spare filter could be more important than having enough gas. The stories of ash in Seattle were mostly a nuisance compared to the 5 inches of ash in Yakima that took ten weeks to remove. That's worse than clearing Seattle's streets after a snowstorm, which makes sense because ash is essentially rock and isn't going to melt.

Volcanoes blow up, not just Mt. St. Helens. Within about the last 200 years, all of Washington's volcanoes except Adams have erupted. The original residents tell tales, and the geological record backs them up. St. Helens has been the busiest, and is building back up, probably to blow again. All of the rest are taller. Taller isn't always more dangerous. Glacier has produced some of the strongest eruptions within the US, and may be the most likely to blow next; though it is more remote. If Baker blows, the ski season will probably change - though there may be some new hot springs. Adams is the second tallest and the quietest, but an eruption would be impressive. And Rainier can't be ignored. It is the biggest, the closest, and even a small eruption would be a big event.

Any of the eruptions will produce ash, and there's no way to avoid it except to hope the wind blows the other way.

The issue that can be kept in mind when shopping for a home are the mud flows called lahars. Lahars aren't limited to the area around the mountain. The St. Helens' lahars reached I-5. The other volcanoes have had major lahars, but they were from before the population boom. Baker's lahars reached what is Bellingham Bay, Mount Vernon, and La Conner. Glacier's reached Mount Vernon, La Conner, and Stanwood. Rainier's reached Kent and Tacoma. Adams' reached the Columbia. Lahars are Mother Nature's earthmovers, filling valleys and flattening the land at up to 60 mph, regardless of the traffic lights. Even if you don't live in a lahar zone, even a small one can ruin your commute.

Every region has its issues: hurricanes, blizzards, tornadoes, droughts, earthquakes, tsunamis, etc. Seattle's mix is mostly geological. The weather is mild; but the ground moves, sometimes as quakes, sometimes as ash, sometimes as mud. The important thing is to be aware of which risks to prepare for, and that changes with location. The USGS is getting better at predicting risks and monitoring current situations, and the next time won't be the same as the previous time. Take what they and other organizations have collected and simply be prepared - and, if you're in Orting and the siren goes off, don't try to get a front row seat. The Oceala lahar was over a hundred feet tall. Oh yeah, and maybe it's a good idea to throw an extra air filter into the car, and maybe face mask for you, too.

http://seattle.curbed.com/archives/2014/10/are-you-ready-for-our-volcanoes-ash-and-lahars.php