In a recent blog article on Mt St Helen’s 31st anniversary, I discussed a visit to the Mt St Helens National Volcanic Monument and displayed some images of earlier 2006 volcanic steam activity. Today, in 2011, Mt St Helens today is relatively peaceful. The U.S.G.S. Cascade Volcano Observatory has assigned it a “normal” rating (since July 2008) reflecting its relative quiet. The explosive eruption (and buildup) of May 18, 1980 is far behind us, and the volcano has left some distance between the eruptions of 2004-8 and today. The image shows clouds dancing across the crater, not steam of volcanic origin.Indications are that Mt St Helens will continue its eruptive activity and is likely to erupt again in this century. (Mt St Helens - A 30 Year Legacy of Volcansim - EOS-AGU). This is based on its age and past history.In my last article, “Calculating Odds and Probabilities” I discussed the assessment of various odds and probabilities ranging from coin tosses to weather forecasting. It is clear that some predictions are relatively straightforward and others are incredibly complex. The events, risks and probabilities associated with volcanic hazards present a great challenge because of the wide ranging risks, the variability of impacts and the low probabilities of occurrence associated with very high impact events.Mt St Helens showed us in 1980 that a low probability, high impact event can happen in our lifetime and region (Washington State). While Mt St Helens is the most active of Cascade Volcanoes, the other Cascade Volcanoes are also of interest.The USGS provides an interactive map of the Cascade Volcanoes from Washington to Northern California. The summary provides a broad overview picturing the scope of Cascade Volcanoes throughout the region. The map/page provides links to each of the Cascade Volcano “Visit a Volcano Site” providing a photo and information for each volcano. The difficulty in assessing the risk associated with an event, whether it is meteorological or seismic, is in assessing the probability that it will occur, the severity of the event should it occur, and the impact on the population.The USGS has done a great deal of work in identifying hazards for the Cascade volcanoes. The Mount St Helens eruption, and other volcanic eruptions have allowed geologists to gain a great deal of information regarding volcanic hazards, and develop advanced monitoring technologies to allow them to better manage volcanic risk.A USGS Fact Sheet (What are Volcano Hazards?) describes Volcano hazards, both in text and with a graphic that displays the hazards on a simplified Cascade volcano. The hazards shown in the Fact Sheet include hazards that we saw with the 1980 Mt St Helens eruption. The pyroclastic flow that blasted down numerous trees, scorched others and killed people. The towering ash cloud that rained ash fall on Eastern Washington and continued around the world. The debris flows that sculptured the landscape in destructive lahars , racing down the Toutle River, washing out bridges and silting up the Columbia River.
In addition, we see the impact of much earlier lava flows in Mt St Helen’s Ape Cave Lava Tube. Ape Cave contains the continental United States’ longest continuous lava tube, occurring around 2,000 years ago in the Cave Basalt.Cascade volcanoes have an extensive volcanic history, as displayed in a display of their eruptive history over the past 4,000 years which is available as a pdf or poster to order from USGS. We can look at the chart of volcanic history and wonder given the frequency and time since last eruption, whether a particular mountain is “due” for an eruption. We do know that future eruptions may occur, we simply may not know when. Once volcanic activity has started, geologists are better able to monitor and respond to the ongoing situation.It is a matter of living with uncertainty and managing risks. The USGS has comprehensive risk assessments for each Cascade Volcano. More information can be obtained through the USGS’s Cascade Volcano Observatory Website.
Aerial View of Steam Eruption, Mt St Helens, May 20, 2006, taken from Johnston Ridge Observatory, Mt St Helens National Volcanic Monument, Washington (image on Photoshelter)Thirty-one years ago, at 8:32 am on May 18, 1980, Mt St Helens erupted, in a cataclysmic eruption, that would change the face of the environment and sow the seeds of future renewal. Nature has its way of promoting renewal, through cycles of creation and destruction, and nowhere is this more evident than at Mt St Helens, where the volcano and environs continue to emerge in their new environment shaped by the vehicles of geological change.Mt. St Helens National Monument can be reach from I-5 southbound at Toledo, SR 505, or from I-5 northbound at Castle Rock, SR 504 (Spirit Lake Highway). I took the latter route, visiting Washington State’s Silver Lake Visitor Center, 5 miles east along SR 504, and took in their presentation on the Mt St Helens Eruption “Cycle of Chaos and Creation”. I entered Mt St Helens National Volcanic Monument, stopping at Hoffstadter Bluffs Visitor Center, enjoying a view of Mt St Helens in the distance and an excellent Elk Burger in their dining area before heading up to Johnston Ridge Observatory. As you drive towards Johnston Ridge Observatory, there are opportunities to pull over and enjoy differing views of the mountain as you get closer, including at the Elk Rock and Loowit Viewpoints. The sense of closeness to the volcano becomes more than distance as you become more and more aware of the impact of the blast area on the landscape. Even as it is being transformed, being renewed, you are aware that there are thirty-one years of renewal, and that contrasts with the age of the landscape you left behind.
Mt St Helens Steam Eruption, May 20, 2006, viewed from Hummocks Trail showing renewal of vegetation, Mt St Helens National Volcanic Monument (image on Photoshelter) The road heads downward before the last ascent to the Johnston Ridge Observatory. The Hummocks Trail provides an opportunity to hike amongst the hummocks, created by the Mt St Helens debris avalanche. The debris avalanche created by the eruption of Mt St Helens offered geologists an opportunity to learn about and identify such formations elsewhere. From the Hummocks Trail, the road then climbs upwards towards Johnston Ridge Observatory at 4,255 feet. As you hike up an incline from the parking lot towards the Visitor Center, you are greeted with a marvelous view of Mt St Helens, looking right down into the throat of the volcano. It is up close and personal, looming as a reminder of the blast impact, as the crater opens up its giant maw to the visitor, you are struck by the awesome power that so forcefully reconstructed the landscape in the wake of its eruption.As the clouds dance across the crater and the lava dome inside it, you are reminded that Mt St Helens, the youngest of Cascade volcanoes, has not been quiet since it’s May 18, 1980 eruption. Eruptive activity continued into 1986 and then resumed during 2004-2006, including dome building activity.A visit to the Visitor Center gives the opportunity to explore exhibits, view a movie, “Message from the Mountain”, and attend ranger-guided talks. In one talk, the ranger used still photographs to illustrate various stages of Mt St Helens’s activity leading up to and including the eruption events. We saw Mt St Helens’s pre-eruptive recreational splendor as a near-perfect volcanic cone and glimpses of pre-eruptive awakenings. As explained by the ranger, volcanic activity beneath the surface of the volcano eroded and weakened the rock structure on the side of the mountain, turning it to clay. This weakened area provided an opportunistic path for the upwelling magma to take, versus the hardened rock plug at the top of the volcano. The side of the mountain bulged with pressure and structural weakening. The landslide and accompanying 5.1 earthquake triggered the event that would unleash the power and fury of Mt St Helens, with resultant lateral blast, pyroclastic flows, lahars (mud flows) and an ejection of ash that would circle the globe.It is sobering to realize that volcanism can eat away at a mountain’s rock structure from within, weakening it and exposing the mountain to risk of collapse. It is yet another example of a “tipping point” where a marginal change can have a result out of proportion to its own magnitude.Geologists and volcanologists study volcanoes and other geological system and we are all continually learning from their experience. Johnston Ridge Observatory was named in memory of geologist David Johnston, volcanologist, who witnessed the May 18, 1980 eruption from what is now Johnston Ridge, and radioed in the message “Vancouver, Vancouver, this is it” before perishing in the blast.The Mt St Helens 1980 eruption has resulted in a continued expansion in knowledge and monitoring tools for understanding the behavior of volcanoes.In one study, the impacts of volcanic hydrothermal systems on Cascade volcanoes is being studied by the United States Geological Survey. A wide range of information about Cascade Volcanoes can be found on the Cascade Volcano Observatory (CVO) site.
