A few weeks back, we heard news of an small earthquake swarm underneath Mount St. Helens. Now, media-driven hyperbole aside, that swarm was business-as-usual for a Cascade volcano, where magma slowly rises back into the upper parts of the system. So, it should be no surprise when other volcanoes in the range show similar behavior. That’s what we might be seeing right now at St. Helens’ southern neighbor, Oregon’s Mt. Hood, where the USGS has noticed a swarm of small earthquakes (all less than M2) that started on Sunday.
It has been over 200 years since Hood’s last eruption, a period that is referred to as the “Old Maid” eruptive period when a small lava dome was formed just off the volcano’s summit. This activity produced some pyroclastic flows that swept down the southeastern sides of the volcano, along with some lahars (volcanic mudflows) that headed down some of the rivers that come off of Hood, like the Sandy River (see below). READ MORE