Life at Mt. St. Helens
September 29, 2006, 3:45 am by Jess. Filed under: explosions, love those goofy b*st*rds.

On May 18, 1980, Mount St. Helens lost 1,314 feet of elevation. In the largest landslide in recorded history, the top and north side of the mountain rolled down into the surrounding landscape. A huge bulge of magma burst sideways through the dome and released a hot, ash- and rock-filled wind that tore through the forest at 350 miles per hour.

The 1980 eruption; USGS photo from wikipedia commons

The blast scorched and ripped up surrounding trees, but no fires started because there was no oxygen. The landslide dammed streams and rivers, creating many new lakes, and left behind whole chunks of the mountain on the landscape. The extreme heat from the eruption melted snow and ice, creating enormous mud flows that took out buildings and bridges. Hundreds of millions of tons of ash were released that day; a vertical column of ash reached fifteen miles up into the atmosphere. 250 square miles of surrounding land were damaged.

The mighty mountain 26 years later; photo by Jess Dolan

Such catastrophes make people think about luck. I was talking with a retired seismologist recently at the Johnston Ridge Observatory, which overlooks the ruptured north side of the mountain. He told me that there was a party in town the night before the blast that all the scientists (except the famous Dave Johnston) attended. Otherwise more of them probably would have been in the “red zone.” He himself had left the Mt. St. Helens area a week before the eruption to study volcanoes in Hawaii.

The ecological recovery of the area has been partly a matter of luck, too. Some organisms were safe, while others had no chance. Stream-dwelling fish were obliterated, overwhelmed by the toxic mud and pumice flows. Migratory salmon, however, were still out in the ocean at this time of year and so were not affected. Fish in frozen lakes were protected by the covering of ice. Large mammals and birds all perished, unable to flee fast enough. But many small nocturnal mammals were sleeping in their underground burrows during the blast, which occurred in the morning. Still-hibernating amphibians and reptiles were also safely burrowed.

The 1980 eruption has given biologists a unique opportunity to study how luck interacts with muck, madness with method, to regenerate an ecosystem. In many ways it is like watching something come out of nothing, like watching life emerge on a barren planet. How it has played out in the last 26 years does not follow any simple model of ecological succession.

Dragonfly; photo from wikipedia commons

On March 18, Spirit Lake was filled in with the avalanche of earth and lava rock, and covered with blown-down trees. No life survived in the lake. But after the work of aerobic and anaerobic bacteria, and the fertilization provided by all the blown-down trees, the lake has been colonized by phytoplankton, algae, insects and amphibians, and is thriving.

On land, things are a lot slower-going. Nutrient-poor volcanic material covers the land where soil used to be. It will be a long time before the forests recover fully. The best places are steep slopes, where erosion uncovered surviving plants and opened the soil for pioneer species like nitrogen-fixing lupine. These plants attract insects and trap windblown seeds. A little clump of life called a “hotspot” forms. When these hotspots enlarge and knit together, the land ecosystem will become stronger. Large scale tree replantings are also contributing to recovery.

At the Mt. St. Helens Visitor Center at Silver Lake, you can see a cross-section of a Doug Fir that was taken down in the 1980 blast, but is thought to have survived the much-worse 1480 blast. You can read the extreme stress in its late 1400s growth rings. Change is the norm for Mt. St. Helens; the volcano became active again exactly two years ago this month. It is fascinating to watch life struggle to emerge from land that, according to Jimmy Carter in 1980, looked more rugged than a moonscape.


4 comments
jump to post comment

Interesting you say that recovery hasn’t followed any simple model of ecological succession; and also that tree replantings are contributing to recovery. Planting trees seems so “helpful” but I’m coming to doubt it.

But first, simplicity. As somebody who used to study succession formally, I can tell you this is yet another subject where those pretty little pictorals in the textbooks (you know, from left to right across a little landscape, you see lichens, then forbs, then shrubs, then trees, then big trees) turned out to be way too idealized.

I think the conviction of this orderly progression might have come from the fact that in the US, much early formal research on succession was done in “old fields” (abandoned from farming). However, most disturbances to ecosystems are far less uniform than farming. Regrowth after, say, a fire, is far more variable partly because of the variability in the intensity of disturbance from spot to spot and acre to acre. That variability is one thing that contributes to the “complexity” in appearance we see decades and centuries later.

Of course, after a disturbance, everybody sees symbolism in the regrowth of trees, like trees are the “goal”. I guess this makes sense because in the age of environmentalism we tend to look at the destruction of trees as bad, so ergo their regrowth is good. Right?

I am becoming more and more convinced that one of the strange legacies of concern for trees is the increasing scarcity of certain ecosystems typical of EARLY succession. For example, in the pacific northwest some species very typical after disturbance are ceanothus (a shrub) and alder (a small hardwood tree, not a classy tree like a doug fir). Foresters will tell you ceanothus and alder domination will delay the emergence of big likeable trees for decades, so, in terms of “recovery,” those species are “bad.”

But the thing is — ceanothus and alder fix nitrogen. They’re enriching the soil. If you plant tree seedlings and do all sorts of other stuff to speed up domination by the big desirable trees, you’re eliminating interesting complexity in the patterns of regeneration. It’s also quite possible you’re impoverishing the soil.

People seem to be equate nature with “cathedral” and “parklike” landscapes — ones with big trees and grass or moss beneath. They forget about those ugly disgusting tangles of ceanothus and salmonberry and other stuff that is generally a mess to look at and punishment to travel through. But in some ways that’s the land of milk and honey…

(not to mention the land of blood dropping from the various perforations I received crawling through these brambles on a journey of “ecological appreciation” — otherwise known as getting completely frikkin lost)

Comment by bottleman on 29.09.2006 um 12:03 pm

Yeah, I think I oversimplified in my coverage of vegetation regrowth. The eruption had several different stages and was a much more complicated disturbance than clearing a flat field for farming.

This site by a Forest Service scientist
http://www.fs.fed.us/gpnf/mshnvm/research/faq.html covers the ecological effects of the eruption thoroughly. He divides the area into five zones based on the level and kind of disturbance and explains how regrowth has played out differently in each one.

Mt. St. Helens is the last place people should look if they want to keep their idea of the balance of nature in tact. Because it is constantly changing, terms like recovery, old growth, or climax community have less meaning. I remember reading somewhere that Mt St Helens will one day return to an old growth forest: what does that mean?

Disturbance is the norm there: it’s amazing to look at the layers of earth at one of the vistor centers: thick layers of volcanic ash and rock interspersed with very thin and sparse organic soil layers. It’s amazing to watch life establish itself there.

What do you think about encouraging the growth of trees and shrubs on areas where one weedy invasive has taken over? In these areas succession is frozen in the early stages for much longer than would have been possible without human trains, planes, automobiles, and boats.

Comment by Jess on 02.10.2006 um 8:40 pm

The idea of Mt. St. Helens returning to old growth forest is a reference to the idea of a site’s “natural vegetative state” or something like that… the kind of landscape you would likely see if disturbance were to not happen again for a long long time…

This is a hoary old idea in ecology, but again, it’s an idea that mostly makes sense in old fields and not in the PNW. If you look at a PNW old growth forest in anywhere but the wettest wettest sites — you will see that the thing we call old growth forest is actually created by partially destructive disturbances. Fires, windthrows, etc, tend to kill some but not all trees, altering the pattern of growth and increasing the variety in sizes of trees in later decades and centuries. That messy variety, including some especially big items, is what we call old growth.

In the PNW there rarely is ever a completely destructive disturbance (though the Mt. St. Helens eruption has got to come close). So really there is no beginning and no end, just constant changes. In one of my last consulting jobs as a biologist, I tried to move my clients away from thinking of succession as a timeline that moves forward towards a “goal”. Instead, I saw it as shifts between possible structural states. Kind of wacky, but definitely a more realistic view.

Should weedy invaders be removed to “speed” succession along? I dunno, I’m sure it depends on circumstances. I guess if you really want more trees fast, then yes. But a number of papers have suggested that a quick return to tree dominance after a major disturbance is NOT necessarily the historical norm for the PNW. It happens sometimes, but not always. Even in lieu of planes, trains, automobiles, there are some sites where tree regen seems to have been held back for decades or even a century. In fact some historical analyses suggest old growth structure emerges sooner from such “poor tree regeneration” sites than better ones… sounds a bit odd, but there are some reasons that makes sense.

I guess I’m just saying that lovely forests aren’t the “goal” of succession; they’re just something that tends to happen. Some people (not you I know :) tend to fetishize that state of the landscape; I’m like “Hey, what about these rocks and lupines?… They need love too!”

Or something. :/

Comment by bottleman on 02.10.2006 um 11:24 pm

wow this is some good stuff im going to the volcanos

Comment by carolpham on 20.10.2006 um 8:27 am



Comment