At the beginning of the semester, I wrote about my connection to Mount St. Helens, the result of a childhood interest in volcanology and a city kid’s first experience with geologic exploration. It was a meaningful part of my childhood. Yet, as a 21 year old, I no longer spend my afternoons obsessively checking the hourly updated images of the volcano, watching for steam and signs of eruptions1. The rocks I collected still sit atop my rock shelf in my childhood bedroom, however they lay amidst a perhaps worrying number of collections from a number of both lab-based and self-guided adventures.
Still, I somehow found myself thinking about Mt. St. Helens just last night. I was in a Zoom call with some friends and we were talking about how remote learning not just makes learning more difficult, but takes a lot of the joy out of the process. It is far less fun to learn about a topic, however cool it is, silently in your room, and then complete a project, however interesting it may be, in solitude. A lot of the joy of learning comes from sharing it, even in little ways. My favorite way of doing work is in a common room with friends, all completing different assignments, occasionally interjecting with how interesting the stuff they are learning is. My friends and I tried to make up for lost time last night, leading to a chaotic 5 hour video chat where we went on Wikipedia deep-dives. I learned a fair bit about the prevalence of yellow birds as witch’s familiars in colonial New England, the economics of unemployment, and the etymology of the word “exit.” I rambled on about my favorite Devonian predators and eventually, ended up on the topic of Mt. St. Helens. My friends had never seen a video of the eruption, so I got to show them the incredible landscape changes that occurred in a matter of seconds. This entire environment of ash and bombs, dried up riverbeds and fallen trees, is so incredibly recent: the 40th anniversary of the eruption is in a few days, on May 18th. I have always accidentally separated settings like Mt St Helens from other geologic environments - this volcano’s effects are so dramatic that it’s hard to imagine them overlain by soil or other deposits.
This class and its talks of cyclic processes has allowed me to view this eruption in a new light. I really enjoyed learning about the Snowball Earth - particularly, the possibility of volcanism causing such a drastic climate change. I decided to do a bit of research into the climate effects of the May 18th, 1980 eruption of Mt. St. Helens. While the eruption was both brief and small compared to that of the Franklin LIP, supervolcanoes, or even 1883’s Krakatoa, it is one of the most studied recent major eruptions. According to Mass and Robock (1981), during the daytime hours following the eruption, the local Washington state temperature was 8°C cooler due to the volcanic plume. The aerosols ejected from the volcano did not rise above the troposphere. Connecting this to the recent readings about the Snowball Earth, it was this eruption, in conjunction with the 1982 eruption of El Chichon in Mexico, that supported the relatively new hypothesis that SO 2 emitted by eruptions (combining with water vapor to form sulfate aerosols) is largely responsible for volcano-induced climate effects. Despite producing significantly less ash, the relatively sulfur-enriched eruption of El Chichon caused 3-5 times the amount of cooling versus Mt. St. Helens (Williams, Washington Post). It is interesting how the climate impact of a volcano is not just a result of ash output. Instead, it is a function of the composition of the ash. It is also largely dependent on the energy balance of the planet: is the volcano near the equator, where radiation input exceeds output and thus blocking the input would have a more drastic effect? This may have been a contributing factor for El Chichon’s effect, however the article did not mention it. Additionally, an important factor is the temperature of the planet: a cooler planet lowers the stratosphere, allowing these sulfur aerosols to reach that layer, enabling the significant blocking of radiation and subsequent climate change. From here, I’m curious about the difference between Mt. St. Helens levels of eruptions at the LGM versus today: could such an eruption, particularly at the equator, have caused any lasting climate effects?
It is also quite interesting that volcanic eruptions produce a means to counteract their effects. Silicate weathering is an incredibly powerful balancing process upon the global climate. While all igneous rocks contain silicates, different types of eruptions affect this process differently. The high volatile magmas of siliceous volcanoes, such as Mt. St. Helens, release a lot of CO 2 and SO 2 into the air and produce a lot of low weatherability andesites and rhyolites. The low volatile magmas of hotspot volcanoes produce highly weatherable rocks while releasing relatively little gas. It would be interesting to compare the effects of silicate weathering on a planet overrun by MORBs and OIBs versus one overrun by the products of explosive volcanism. This discussion also greatly oversimplifies the types and variability of volcanic outputs, which makes this even more interesting.
I also have found myself more interested in the temporality of the Mt. St. Helens setting. We often see images of nature returning to the ash-covered land , which is quite cool to see. However, I think I’m more interested in the geologic evolution of the region. Geologic evolution does not mean millions of years: it too can be quite quick. Many of these lands are protected, so they hopefully will be able to develop without direct human influence. Will weathering produce soils out of the pyroclastic deposits? Larger volcanics can certainly be weathered, but can ash be physically weathered? Or is it too fine to be broken apart? How many organics will have to return to the region (for instance, grasses and trees) before the soil is carbon-rich enough to be viable?
The part of my childhood visit to this region that was most memorable was my journey into a former stream that was now simply a bed of pyroclastic deposits. I found myself fully focused on the present state rather than the implications it holds on the past and the surrounding area. Assuming the river’s source is significantly upstream, where did the river divert to? What happens to a flow of water that is suddenly blocked by incredibly hot ash? Certainly a lot of water will instantly evaporate, but once the exposed rocks cool, where does the water go? I’m also curious about the state of the river today versus in 1980: how has it evolved? The sudden creation of a river certainly would lead to some interesting geology.
Overall, it is important not to just focus on an instant, however exciting, geologic “event” such as a volcanic eruption. There is far more to the story than just that. The lands covered by the eruption are in no way “ruined,” and while such spaces should be accessible for exploration and education, they should not be considered wastelands, lacking futures. Natural processes will allow the region to continue to change; perhaps not as instantly as a pyroclastic flow, but the region never stops changing. Surface and subsurface processes do not cease.
Also, extending this to greater issues of climate, it is important to understand two seemingly contradictory points about our planet. First, the Earth is the host of a great number of balancing feedbacks: weathering in particular helps balance the CO 2 in the air with that stored within rocks. However, the planet is still at risk of drastic, dangerous climate change. Whether caused by humans or by natural events such as volcanic eruptions, events can perturb positive feedback loops, such as ice-albedo-temperature or the many carbon cycle based feedbacks, and amplify climate change. It is important to understand how seemingly small changes can cause such great effects, and how long it will take for the Earth to recover.
Mass, C. and A. Robock, 1982: The Short-Term Influence of the Mount St. Helens
Volcanic Eruption on Surface Temperature in the Northwest United States. Mon. Wea. Rev., 110, 614–622.
1 Yes, I did this, every day. This was in between checking the weather.gov radar for supercells and tornado-bearing hooks and the National Hurricane Center for windspeed forecasts of approaching hurricanes. There was never a point in my life I did not want to become a scientist, haha