Arkansas River GLOF
Thought I would share some info I learned this summer. I took a one day class through the CO. Mountain College in Leadville called "When Ice Ruled Leadville". It was taught by geologist, Dr. Vince Matthews. Awesome day. We spent an hour or two in a classroom and then all jumped in a short bus and went to several locations where we hiked while he lectured about what we were looking at relative to the glacial history of the area. Spent time up Evans Gulch above Leadville observing the upland features. Drove up the Lake Creek drainage and spent time overlooking Twin Lakes. The lakes are created/dammed by a terminal moraine and a recessional moraine. There are lateral moraines 800' above Twin Lakes. The best part,and primary reason for me being there, was our stop at the AHRA putin for the Numbers.
Let me say, I am not a geologist, just a boater with curiosity...
Pine Creek comes in at the Pine Creek rapid. Duh! Its quite a tight valley as is the Ark at that point. Its where the Ark comes closest to the granite wall on river left with the creek coming in on river right. The last glacial period was yesterday in geologic terms. So, 10 or 11,000 years ago the Pine Creek glacier had pushed across the Ark and dammed the rio as it plugged against the river left wall. It created a lake behind it that was 600' deep and 14 miles long! The head of the lake was at Malta! GLOF stands for Glacial Lake Outburst Flood. The evidence suggests that when the glacial dam failed catastrophically the lake drained in as little as 24 hours! This cycle has happened 3 times in the last 30,000 years. You can see terraces and cuts from the several floods all down through the Numbers and Fractions. There are large rocks as far down river as Salida from these events.
One extrapolation I've made is that since the entire rio bed was deposited, arranged and rearranged by this last event, it means that the beautiful sculpting of the granite boulders that we see, usually on the downstream side, has all been done in the last 10,000 years. Maybe I'm just getting old but that is a human scale of time.
Anyway, this all has certainly changed how I look at and experience the river. What a beautiful paradise we have to paddle in.