Long-term melt threat to infrastructure; “good engineers” needed

North Slope oil operators face a long-term, existential threat to infrastructure for which there is no easy solution – thawing permafrost. It’s a challenge but it will also stimulate a lot of thinking about essentially rebuilding parts of the slope into what could be more like an offshore field. Scientists at the University of Alaska Fairbanks’ have been taking deep temperature measurements in permafrost soils underlying the producing oilfields on the slope and along the Trans-Alaska Pipeline System. Since 1978, when measurements began, temperatures at the 65-foot depth have shown steady warming with the steepest increase at 6 degrees F in the oil fields at the northern end of TAPS. In 1978 the permafrost at 65 feet near the Prudhoe Bay was about 16.3 degrees F. As of this year it has warmed to 22.6 degrees F.

Thaw points in 2050 and 2100
In a new report recently published by the university’s Geophysical Institute the warming has been projected forward for the first time. If the rate of warming continues at current rates the melt point at 32 degrees F would be reached in 2100 at 65 feet, modeling suggests. The rate of change correlates with the rising atmospheric temperatures in the Arctic, which is related to climate change, UAF scientists told us. The 65-foot depth was selected for measurement because this is deep enough to be unaffected by seasonal freeze-thaw cycles. What’s important for industry is that the melt point will be reached much earlier at shallower depths. By 2050, three decades from now, many ice-rich silty soils underlying the North Slope will be at 32 degrees F, essentially turning into silt slurry. That’s because water absorbs heat more efficiently and acts as an accelerator in melting, the scientists said.

Most of slope built on ice-rich silt
Most of the North Slope is underlain by ice-rich silt that extends to bedrock. The depth of bedrock varies but it’s deep in many places, and the mostly-organic material in the silt tends to collect water. There is a lot of ice in the first 20 to 30 feet of material that is particularly vulnerable to thaw. If the thaw extends down 15 feet to 30 feet the soils below surface infrastructure like roads and airports become unstable. There are also massive pure ice wedges, some as deep as 90 feet and, when these thaw, soil subsidence can happen quickly. Instances of five and six feet of sinking in one year have been observed. Even two feet of subsidence can cause a lot of problems and this could occur faster than people think, the UAF scientists told us.