By David Wartinbee, for the Redoubt Reporter
On a clear day from just about anywhere on the Kenai Peninsula, we can see two of the dominant peaks across the inlet, Mount Redoubt and Mount Iliamna. I don’t mean to ignore the more northerly Mount Spurr, especially since it is about 1,000 feet taller than either of the other two. However, Mount Spurr just doesn’t stand out so starkly against much lower background mountains the way Iliamna and Redoubt do.
If you have lived here or visited the peninsula in the past, I’ll bet you have a couple photos of these two picturesque mountains. I have a collection of Mount Redoubt and Mount Iliamna pictures that number in the hundreds and date all the way back to 1977.
When I look back at these pictures, no matter what time of the year they were taken and no matter how close I was when I tripped the shutter, they all show a 10,000-foot white mountain. But not today. If you take out your binoculars on a clear day this summer you will find that Iliamna is still snow-covered and white but Redoubt is dark with only a hint of white in selected spots. Redoubt has belched ash all over its normally pure-white bib.
The recent eruptions of Redoubt have caused a couple noteworthy events, and, in turn, these have impacted a number of surrounding streams. The most catastrophic activities were the formation of lahars. Secondarily, the ash itself is finding its way into many streams, and this can also disrupt the stream ecosystems.
Lahars are a volcanic version of a flash flood or mud flow. In areas close to Redoubt, where heated pyroclastic flows melted large sections of glacial ice and snow, lahars were formed, primarily on the north side of the mountain. Lahars can include large amounts of ash and ejected materials, ice chunks that broke off but didn’t yet melt, and huge volumes of meltwater. They flow downstream with unimaginable force and are aptly described as fast-flowing concrete. The concrete description conjures up a vision of the material eventually setting up and becoming a solid mass.
That’s about what lahars do. (I have vivid memories of seeing upside-down tree trunks sticking out at odd angles from the now solid flood plain substrate, still frozen in place, five years after the Toutle River endured a lahar caused by the Mount St. Helens eruption in 1980.) Lahars can cause river channels to wildly diverge from previous directions. That’s what happened to the Drift River this year. From the air, one can clearly see that the water paths are different than they were a few months before. Incidentally, changes in the Drift River channels were one of the major disruptions that happened after the 1989 Mount Redoubt eruption, too. Just like in 1989, the riparian vegetation surrounding Drift River has been heavily scoured by this year’s lahars and little vegetation remains in the flood plain.
This spring, we heard news reports about how these lahars pushed mud, ice, silt and remnants of vegetation against the retaining wall protecting the Drift River oil storage tanks. The lahars also covered the facility airstrip so planes could no longer land or take off.
Changes in riverine channels can be disastrous to the fauna of any stream or river. Five years after the 1989 Mount Redoubt eruption, scientists found that Drift River was slowly recovering, and we can expect that today the normal fauna is just starting a recovery, as well. The Drift River fauna will be relatively slow to recover until the substrates can stabilize and predictable flow patterns become established.
Because Drift River normally has the inherently unstable substrates of glacier outflow streams and the low temperatures of the water under the best of conditions, the pre-lahar fauna was probably limited to begin with. So, for another decade or so, we can expect the diversity of Drift River organisms to be even lower and dominated by chironomidae midges like diamesa that do well in cold-water, unstable substrate streams.
From the studies done on the Drift River after the 1989 eruptions, we would predict that the overall aquatic insect diversity would be low and, specifically, there will probably be a limited number of mayflies, stoneflies and caddisflies there today.
There is a concern that an ash fall might change the chemical scent of a stream and returning salmon may not recognize their natal stream. It has been observed that after volcanic ash releases in the Northwest states, there were more “stray” anadromous fish that were apparently looking for their home stream. They also noticed modest reductions in the overall numbers of fish that returned. Those areas of Drift River that suffered the most disruptive lahars were probably the areas least able to support fish populations, so I don’t expect a major loss there. However, any salmon that may have come from more stable side channels of the Drift River complex could have difficulty finding their hatching site when they do return.
Lahars can sometimes deposit materials that are dozens of feet thick. It might take years for the stream to erode through that new material and return to a more normal and more stable habitat. Because of deposits in some areas and new channels in others, we probably shouldn’t look for a return to the original Drift River fauna for many years to come.
David Wartinbee, Ph.D, J.D., is a biology professor at Kenai Peninsula College’s Kenai River Campus. He is writing a series of columns on the ecology of the Kenai River and Cook Inlet watershed.