Post by slh1234 on Sept 23, 2010 13:30:05 GMT
I wanted to post a few lines from what caught my attention on my last trip to the Mendenhall Glacier near Juneau, Alaska the first week of September. These are by no means exhaustive, they're just a few things that I found interesting and thought someone else might like to comment on.
During the film at the Visitors' Center, they put the beginning of the "Little Ice Age" at about 3000 years ago. This is the first time I've heard that time as the beginning of the LIA.
The Mendenhall glacier reached its maximum known extent about 250 years ago, and began retreating at that time. So it has been retreating for about 250 years.
According to one of the rangers, about 90% of the glaciers in British Columbia and Alaska are retreating, and 10% are advancing. The difference between the advancing and retreating glaciers is the altitude of the ice fields that are the collection areas for the glaciers. Those with collection areas above 5000 feet (about 1524 meters) are advancing, and those with collection areas below 5000 feet are retreating. I took the 5000 to be a round estimate of course. This one is unexpected as I think about this more since I thought the retreat or advance would be more about precipitation and temperature along the glacier path rather than the altitude of the collection fields. I thought about precipitation in the collection fields as affecting the extent because it increases the volume of ice, and temperature along the path would affect the rate of melting, but if the ice is ice at collection, then the correlation with altitude is a bit surprising to me.
In 1935, you could touch the face of the Mendenhall glacier from the current location of the visitor's center. It is now over 1 mile from the visitor's center to the terminus.
Mendenhall glacier is currently retreating at about 60 feet/year (about 18.2 meters/year).
The area where the visitor's center currently sets it rising at about 1/2 inch (about 1 CM) per year. (This is also about the same rate that the Teton Mountains in Wyoming are rising)
As glaciers retreat, life quickly returns to the area it once occupied. This is especially true in the rainforest biome of the Juneau area. LIchens move in first and are followed by other plants and animals quickly. The first plants are eventually crowded out all together by the more advanced plants and animals that follow. Life thrives in the areas exposed by the retreating glacier.
It takes over 200 years for the glacier to travel the 13 miles from the ice field to the terminus.
So those are the ones I'll leave to discuss from that trip. The ones that I found surprising were placing the beginning of the LIA at 3000 years ago, the glacier retreat starting about 250 YA (Previously, I thought it was about 200), and the correlation between the altitude of the collection areas and whether glaciers are retreating or advancing in Alaska and British Columbia. I'll also say that if anyone visits, the visitors center and the film are very good. They are about as apolitical as anything I've seen on the topic (People's reactions to it are not apolitical, but the presentation of the information is).
I'd like to year other people's thoughts or experiences from there or other glaciers.
During the film at the Visitors' Center, they put the beginning of the "Little Ice Age" at about 3000 years ago. This is the first time I've heard that time as the beginning of the LIA.
The Mendenhall glacier reached its maximum known extent about 250 years ago, and began retreating at that time. So it has been retreating for about 250 years.
According to one of the rangers, about 90% of the glaciers in British Columbia and Alaska are retreating, and 10% are advancing. The difference between the advancing and retreating glaciers is the altitude of the ice fields that are the collection areas for the glaciers. Those with collection areas above 5000 feet (about 1524 meters) are advancing, and those with collection areas below 5000 feet are retreating. I took the 5000 to be a round estimate of course. This one is unexpected as I think about this more since I thought the retreat or advance would be more about precipitation and temperature along the glacier path rather than the altitude of the collection fields. I thought about precipitation in the collection fields as affecting the extent because it increases the volume of ice, and temperature along the path would affect the rate of melting, but if the ice is ice at collection, then the correlation with altitude is a bit surprising to me.
In 1935, you could touch the face of the Mendenhall glacier from the current location of the visitor's center. It is now over 1 mile from the visitor's center to the terminus.
Mendenhall glacier is currently retreating at about 60 feet/year (about 18.2 meters/year).
The area where the visitor's center currently sets it rising at about 1/2 inch (about 1 CM) per year. (This is also about the same rate that the Teton Mountains in Wyoming are rising)
As glaciers retreat, life quickly returns to the area it once occupied. This is especially true in the rainforest biome of the Juneau area. LIchens move in first and are followed by other plants and animals quickly. The first plants are eventually crowded out all together by the more advanced plants and animals that follow. Life thrives in the areas exposed by the retreating glacier.
It takes over 200 years for the glacier to travel the 13 miles from the ice field to the terminus.
So those are the ones I'll leave to discuss from that trip. The ones that I found surprising were placing the beginning of the LIA at 3000 years ago, the glacier retreat starting about 250 YA (Previously, I thought it was about 200), and the correlation between the altitude of the collection areas and whether glaciers are retreating or advancing in Alaska and British Columbia. I'll also say that if anyone visits, the visitors center and the film are very good. They are about as apolitical as anything I've seen on the topic (People's reactions to it are not apolitical, but the presentation of the information is).
I'd like to year other people's thoughts or experiences from there or other glaciers.