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Debris Avalanches at Mount Baker

Hydrothermally altered rock of Sherman Crater's western crater wall, Mount Baker, Washington. (Credit: Scurlock, John. Public domain.)

Small debris avalanches of rock, snow and glacial ice are fairly common occurrences at Mount Baker with or without accompanying volcanic activity. Tens of events have taken place in recorded history (all less than 500,000 m3, 650,000 yd3, or 200 Olympic pools), none of which have traveled more than 3 km (less than 2 mi) downslope. In the past century, these small debris avalanches all originated near Sherman Crater, an area of highly weathered and fractured hydrothermally altered rock. Such minor events only pose a threat to those in the avalanche path.

Two larger debris avalanches have gone down Rainbow Creek in recent years – around 1890 and again around 1930. They were big enough to generate debris flows downstream and, if they occurred again today, could have significant impacts on roads, reservoirs, travelers, and salmon and other aquatic habitat.

Much larger sized (volumes up to 0.1 km3 0.02mi3, or 40,000 Olympic pools) debris avalanches have moved down Rainbow Creek valley in the last 600 years; the largest of which traveled about 9 km (6 mi) from its source. Deposits of this debris avalanche form a hummocky surface on the valley floor where small ponds and lakes occupy depressions between hummocks – the largest is Rainbow Lake. Additionally, many of the clay-rich lahars, including the large Middle Fork Nooksack lahar, are interpreted to have originated as debris avalanches during eruptive periods.