The Geology of Glacier Bay National Park
Almost 100 Years Old, Park is Losing Glacial Coverage
Jun 29, 2009
Glacier Bay National Park, located in southeast Alaska, is one of the most remote and wild national parks in the United States. Accessible only by boat or plane, this park has been a popular destination in Alaska since it became a national monument in 1925. Every year, nearly half a million visitors – cruise ship passengers, tour boat passengers, land visitors and backcountry hikers – come to this beautiful park to view glaciers that are hundreds of thousands of years old. But recent climate activity is changing the landscape of this park.
The Geology and the Landscape of Glacier Bay
The geology of Glacier Bay can be described as many dynamic process. Below the surface, continental plates converge at a rate of several centimeters per year. On the surface, moving glaciers erode and deposit bedrock, carving out valleys and shaping the landscape.
Glacier Bay lies on top of a tectonically active region of the world referred to as the "Ring of Fire". Along the west coasts of South America, Central America and North America, the Pacific plate is generally being subducted under various continental plates. This same process is occurring underneath Glacier Bay where the Pacific plate is sinking below the North American plate. However, in this area, instead of one plate cleanly sinking under another, pieces of both plates are crunched together so that they produce a geologic feature called terranes. A terrane is a piece of crust that has broken off one plate and attached itself to another. Four terranes make up Glacier Bay National Park.
The converging and compression of these two plates has also produced mountain ranges. There are multiple mountain ranges throughout Glacier Bay. One of these ranges, called the Fairweather Range, has several peaks over 10,000 feet. The tallest of these peaks, Mount Fairweather, is 15,300 feet, making this range the highest coastal mountain range in the world.
Glacial Coverage in Glacier Bay
Recent satellite data of Glacier Bay compared to ground observations taken since the 1800s show that the glaciers in this park are receding, some more quickly than others. In order for an ice field to qualify as a glacier, it must be at least 25 acres in size. In 1900, there were more than 150 glaciers within the park that met this size criterion. Now there are only 25. The Muir Glacier was once one of the grandest glaciers in the park, but recent climate change has severely impacted it. Where once it extended into the ocean, referred to as a tidewater terminus, it now terminates well inland so that vegetation and animal life have flourished along the coasts of the Muir Inlet.
Increase in sea level from melting glaciers on Greenland and Antarctica would have the greatest impact globally. But if all the glaciers in Glacier Bay National Park melted, this would cause a sea level rise of almost two feet.
Sources:
Understanding Glaciers of Glacier Bay Alaska
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