A state department of natural resources geologist was in town with a crew last week, to finish the LIDAR mapping of the slopes around Haines. The crew could not map above a thousand feet during previous visits, this time they hit the right weather window to finish collecting data.
The analysis of the imaging will not be completed until next summer, but DNR geologist Dr Ronald Daanen had a chance to observe the slide at 23 miles, and warned about melting permafrost. Haines is not usually associated with permafrost, but there are two kinds, one found around the arctic, and alpine permafrost, which occurs at altitude.
“There is permafrost up there and the frozen ground keeps a lot of this material in place. I have some evidence, from a station that we placed on Takshanuk in 2016, and it showed that the mean annual ground temperature was blow freezing, the other evidence we have of this is that on the north facing side of Takshanuk we see glaciers at the same elevation as the catchments where the material are falling. Also, on the south facing side, there are rock glaciers, and these are what we call periglacial features”
Both kinds of permafrost are melting on our warming planet, but alpine permafrost is melting faster, according to an article by the National Science Foundation.
This is bad news for the near future, as melting permafrost releases carbon dioxide and methane, which contribute to climate change. It is also bad news immediately, as a couple of northbound drivers found out last week when their car was buried in the slide at 23 miles, as reported in a Chilkat Valley News article.
The overall warmer temperatures in the last few decades in this part of Alaska have caused the permafrost to degrade or partially melt, destabilizing the slopes and making rockslides more likely. This has been extensively studied in Glacier Bay by the US Geological Survey.
Dr Daanen said that contrary to a normal landslide, where land falls once and then some stability can be expected, “In the case of debris flow, it’s slightly different in that the material builds up in the channel over a long period of time, and then it releases down the channel” and a lot is yet to come down ” Yeah, it’s more like ninety percent is still there.”
Comparable to water in a river delta, sliding debris can skip channels unpredictably, potentially endangering nearby habitations. Dr Daanen said that DOT has a role to play in keeping the slide areas at 19 and 23 miles as safe as possible. He recommends periodically monitoring slide areas and that DOT keep maintaining the current channel so the rocks follow a predictable path.
“I know nobody wants to hear this, but it could happen any day again, even though a large debris flow just happened, if the rains come back in similar quantities…”
Below is audio of the full interview with Dr Daanen, and links to related articles and papers
