Submitted by Anonymous on Wed, 05/19/2010 - 09:10
Forums
Early Human Settlement in Arctic Alaska

Hi Karl- great looking activity! In addition to the Bering Strait being above water during the last ice age due to low sea level, can you comment on how/why it was glacier-free?

Keep up the great work and have a fantastic ending to the school year. Best- Bill

Thu, 06/17/2010 - 20:56

Karl Horeis

I apologize for the long delay, Bill. I have to admit: you stumped me! I have wondered that same thing. I taught the students about how the glaciers came all the way down to Kansas during the ice age (that's why there's such nice, nutrient-rich glacial till deposited there to grow all that corn) but I wondered, "How did people travel through NW Alaska at that time without snowmobiles? Wouldn't they freeze?"My initial response was that there must have been snow and ice where the dig will be and that people must have crossed the snow. But in order to find a better answer for you, I asked one of the chief researchers on our project, archaeologist Bill Hedman of the Bureau of Land Management's Central Yukon Field Office. Here's what he had to say:
"The Raven Bluff site was probably sitting very near the margin of alpine glaciers coming down the valleys of the DeLong mountains. Within a few miles of the site are several u-shaped valleys and moraine deposits left by retreating alpine glaciers. In other areas, truly vast areas such as most of Canada, northern Europe, and Siberia, the land was covered by ice over a mile thick in places. These vast sheets of ice are continental glaciers. Most of the atmospheric water comes from the oceans. If it keeps falling as snow, turning into ice, and thawing very little in the summer, the oceans drop. I think about 100 meters is a ballpark on the drop during the Wisconsin Ice Age (the last one). If I remember my geology, the Wisconsin Ice Age peaked (glacial maximum) something like 26,000 years ago and climate began ameliorating by about 18,000 years ago (you can check this online to check the dates). If you take your question to the next level of complexity, ask why we didn't have a continental glacier in interior Alaska. I'm not going there. I can make some things up, but you should go to a proper geologist with that one."
I hope that helps, Bill. Thanks again for the great question!
Karl

Fri, 06/18/2010 - 11:39

Anonymous

Glaciers are as much or more about moisture (in the form of snowfall) as they are about cold. So even though this high latitude region was sufficiently cold, the reason that glaciers did not form on the Bering Land Bridge is largely because of the lack of snowfall. The Bering Land Bridge was the center of a large land mass and had a dry interior, or continental climate. The land bridge was also relatively flat and at low elevation, which prevented even localized alpine glaciers from forming as they did further east in the Brooks Range.Here is a nifty animation of the flooding land bridge done by researchers at the University of Colorado: http://instaar.colorado.edu/qgisl/bering_land_bridge/
Pay attention to the map at the 11,000 year mark and you can see that the land bridge was still largely intact at the time the Raven Bluff site was occupied. I would be surprised if the people who occupied this site had not regularly ranged onto at least the eastern edge of the land bridge.
Here are some good map resources for glaciers in the Brooks Range and across Alaska:
http://instaar.colorado.edu/QGISL/ak_paleoglacier_atlas/gallery/index.h…
Jeff

Wed, 06/23/2010 - 12:47

Karl Horeis

Thanks for jumping in, Dr. Rasic. I had no idea the land bridge was sowide. The word "bridge" has always made me picture a narrow strip, but
the animation shows it was about 1,000 miles across at its widest point.
So the area where we'll be digging wasn't a coastal peninsula at all but
actually a vast, open inland ecosystem. I'm so excited to go see it in
person in a few weeks!