Communities in the Pacific Northwest are no strangers to volcanoes, with many of the region’s towns and cities overshadowed by seismically active peaks. Yet while eruptions usually give locals time to evacuate, another type of volcanic catastrophe has the potential to devastate nearby populations without warning – and could occur at any time.
Known as lahars, these deadly events are essentially enormous landslides that occur as the inherently unstable slopes of volcanoes tumble and fall. Lahars that are unleashed in the wake of eruptions are usually predictable, but a far more sinister variety known as “no-notice lahars” has got local authorities particularly worried.
These unannounced rockfalls can be triggered by a range of factors including the weather, as storms or heavy rain can sometimes melt the ice that holds together the rocky debris and sediment that sits atop glaciated volcanoes. Colossal landslides can quickly ensue, catching nearby communities completely unaware.
According to the United States Geological Survey (USG), around 20 percent of all volcano-related deaths have been caused by lahars. In recent times, the most devastating of these occurred in May 1980, when a torrent of rock and earth cascaded down the flanks of Mount St Helens, claiming 57 lives.
The USGS recently issued a warning about the potential for far-reaching lahars at Mount Adams, which is currently showing elevated levels of activity. According to Popular Mechanics, some 60 lahars have also originated from Mount Rainier over the past 10,000 years.
In a desperate attempt to gain advanced warning of no-notice lahars, the Cascades Volcano Observatory (CVO) has set up over 20 monitoring stations along the length of the Cascades Range, which stretches from British Columbia to California. Equipped with cameras, tripwires and a range of other instruments for detecting ground movements, these outposts provide vital real time updates that could help the authorities catch a lahar in the minutes before it reaches nearby communities, thus providing an opportunity to organize a last-ditch evacuation.
Even if a lahar is detected early on, though, time will still be of the essence. In Washington state, for example, a lahar on the western slope of Mount Rainier could engulf towns like Orting, Puyallup and Sumner in as little as 30 minutes.
Evacuation drills in schools are common practice in communities along lahar paths. Let’s hope that if disaster does strike, these rehearsals are put to good use and everyone manages to get out of town safely.
[H/T: Popular Mechanics]
