The most fascinating part is the timing of flooding of large areas after the ice retreated. During the ice age sea levels were much lower. The western Washington coastline extended many miles out to the west. Local sea level in Puget Sound at the end of the ice age can be tricky to figure out. As the ice age was ending sea levels were rising due to ice melt. However, the mass of glacial ice in the Puget lowland had depressed the local earth surface downward. There was a delay from the time of ice retreat to full flooding by sea water and then as the land rebounded flooded areas emerged. In the Bellingham area on the northwest portion of the map, local sea level was as much as 600 feet above the current local level. At that time there was significant ice floating on the sea water and as the ice melted it rained silt and clay onto the sea floor below. Much of the low lands of Whatcom County are mantled with this sea floor deposit.
The still picture I saved is of particular interest to me as I do a lot of work on the northwest portion of the Olympic Peninsula. The picture captures the period of time when the ice lobe was still blocking the outlet to the sea and what is now Puget Sound was a fresh water lake called Lake Russel. Just where did the lake drain to the north when the ice retreated? Ralph Haugerud has suggested the Chimacum Valley as being the outlet. My thoughts are that it may be more complicated and the drainage may have taken place in phases, but I do concur that a surge of water went down the Chimacum Valley at some point. The film does show that the ice edge hung up for at least a little while near Port Townsend and that is very consistent with my observations of the deposits in the Port Townsnd area.
No comments:
Post a Comment