by Dahlia Gietka

My name is Dahlia and I am a Trip Lead for Peaks and Professors. This quarter, winter 2024, I took a class called “Living With Volcanoes”, in which we learned about a number of volcanoes that have erupted recently (in geologic terms), including our local Mount St. Helens (located about 200 miles south of Seattle)! This quarter, I was also fortunate enough to be able to summit Mount St. Helens with a group of Peaks and Professors trip leads. Both of these experiences have exposed me to how incredible Mount St. Helens is! So, today I share with you the history of Mount St. Helens, the highlights of the 1980 eruption, and cool features you can look out for if you decide to climb Mount St. Helens yourself!

A selfie with Jessica, Isabelle, and Will on a trip lead adventure to St. Helens

Mount St. Helens is located at an oceanic-continental plate subduction zone, which has been the cause of the creation of the mountain range we’ve grown to love: the High Cascades! The High Cascades have been around for 38 million years, and has been the location of many volcanic eruptions, both calm and explosive. But, the most notable eruption of the Cascades has been Mount St. Helens in May 1980. Leading up to this devastating eruption, seismologists detected over 10,000 earthquakes within the span of March-May 1980. Additionally, a “bulge” on the side of the mountain was being monitored; it was recorded to be growing by 1.5 meters per day. This “bulge” was indicative of magma coming up from below the Earth’s surface and into Helens’ above-ground mountain feature. Geologists also detected the magma traveling underground using satellite imagery. After this extensive period of preparation, Helens erupted on May 18th 1980. The eruption began at 8:32 am with a 5.1 magnitude earthquake, a huge chunk of the mountain sliding off of the side flank, and a vertical eruption column. At 8:50 am, a debris avalanche (or lahar) ran down the side of the mountain, burying homes in about 50 meter deep mud (with boulders, trees, etc. in it). The eruption continued as landslides and blasts until 5:15 pm. This extreme event led to 35 deaths and 22 missing people, as well as $2.7 billion in damages (roads, railways, bridges, agricultural loss, damaged machinery, and timber loss). Since 1980, vegetation has mostly returned to the mountain and recreation areas have been reopened. But, Helens will never be the same again.

The events of May 1980 changed Helens significantly, creating some fascinating features for geologists and hikers alike! If you ever visit Mount St. Helens, here are some cool features to keep your eyes peeled for. First, of course, is the huge crater at the center of the mountain where the material was blasted off. Don’t get too close to the edge of the crater (especially in snowy conditions!), but I would highly recommend getting a peek if you can! The crater is slowly being refilled with material as Helens gently extrudes more magma, so it won’t be there forever! Another feature I would look out for is the hummocky topography created by the eruption’s mudflows. “Hummocky topography” refers to the small (~15 meters high) lumpy hills at the base of the mountain. These hills are made of the mud and rocks that slid down the face of Mount St. Helens on the day of the big eruption. Lastly, you can notice how young the trees on/around Mount St. Helens are. Since all of the trees on the mountain were scorched or pulled out of the ground (by avalanches) on the day of the eruption, all of the trees currently on Mount St. Helens are from 1980 or sooner (aka 44 years old or younger). You won’t see any old-growth trees on your next Mount St. Helens adventure! Happy trails!

Mount St. Helens

Mountain Wo(men)