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EarthCache

Exit Glacier

Hidden : 7/6/2010
In Alaska, United States
Difficulty:
2 out of 5
Terrain:
2 out of 5

Size: Size: not chosen (not chosen)

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Geocache Description:


Exit Glacier is the only glacier readily accessible by road from the Seward area. It is part of the Kenai Fjords National Park. Once at the parking coordinates, please park safely and follow the well marked paths to discover more about this fascinating geological landmark. In order to preserve this unique experience for yourself and others, it is important to stay on the marked paths. No part of this Earthcache will require you to leave the paths or other developed park areas.

Exit Glacier is one of the approximately 40 glaciers that descend from the Harding Icefield. The Harding Icefield covers over 300 square miles of the Kenai Peninsula and is the largest icefield fully contained within the United States. Exit Glacier received its name as it is the preferred exit point for expeditions which have explored the Harding Icefield.

Both glaciers and icefields occur where the rate of snow accumulation is greater than losses through melting and sublimation. As snow accumulates, earlier deposits are buried deeper and deeper. As this happens, they experience ever higher pressures. These pressures compress the snow, rather like compacting a snowball but on a very large scale. After enough pressure has been applied, the snow turns to granular ice called firn. Under even greater pressure, the firn turns to dense, crystalline ice. It is this glacial ice which forms the body of both ice sheets and glaciers. This glacial ice contains thousands of minute trapped air bubbles, which help give glacial ice its characteristic blue color. The blue color is because the ice absorbs all but the shortest wavelengths of light.

Icefields form in geologic basins or flat topographic areas. Glaciers form on slopes. It might be helpful to think of icefields as solid ice lakes, while glaciers are rivers of solid ice. Under great pressure, ice behaves like a plastic solid rather than the brittle behavior that we are all familiar with. Glaciers move under their own weight due to gravity. Some motion is through the plastic deformation of the ice itself, while another part can be from the slight melting of the ice which can occur at the base of the glacier. This melting allows the glacier to move over a thin film of water, in a much slower version of what happens beneath an ice skater’s blade.

Glaciers have two areas: the accumulation area and the ablation area. The accumulation area is where the snow is accumulating and being turned into glacial ice. The ablation area is the area where most of the melting takes place. It is important to note that the ice that makes up a glacier is ALWAYS either moving downhill or, in special cases, holding still. The ice itself never retreats uphill. However, the terminus or toe of the glacier will change position throughout the year and over the course of multiple years. If the rate of snow accumulation is greater than the rate of melting, the toe will move down the valley and the glacier is said to be advancing. If the rate of melting is greater than the rate of snow accumulation, the toe will move up the valley and the glacier is said to be retreating.

Exit Glacier, as noted, originates in the Harding Icefield and flows down the valley towards the ocean. At present time and throughout recorded history, Exit Glacier has terminated on land well short of the shoreline. Throughout history, this termination -- or toe -- has fluctuated year to year, as noted by signs bearing years along the road approaching the Visitor Center, and along the trail.

Below the toe of Exit Glacier, a broad plain can be seen. If you look at it carefully, you will see that it is full of small stream channels, diverging and rejoining with each other, separated by sand and gravel hummocks and bars. This plain is called an outwash plain and the river that flows in it is called a braided river. Braided rivers form when there is more sediment than the water can easily carry.

The passage of glaciers over the bedrock surface can smooth and polish these surfaces to a remarkable degree. If you keep your eyes open during your hike, you can see a number of examples of this glacial polish on the exposed bedrock outcrops. You can also see scouring: scratch marks as would be left by, say, rough sandpaper on hard soap, which also tells of the glacier's passage, and the force it exerts on the rock beneath it.

Another interesting feature of glaciers is their ability to carry large boulders many miles from their point of origin. Some of these boulders can be the size of a house or even larger. These boulders, called glacial erratics, may be found perched on the landscape like abandoned toys with no obvious clue as to where they came from or how they got there.

Waypoints:
Parking: N60 11.321 W149 37.845
Glacier View: N60 11.041, W149 37.946
Braided River View: N60 10.931, W149 38.411
Glacial Polish: N60 10.874, W149 38.580
Glacial Erratic: N60 10.901, W149 38.558

Logging Requirements:
In order to log your visit to this Earthcache, you must do the following:
1) Have a good time and enjoy your visit to beautiful Exit Glacier! Please remember to stay on the paths and to respect the park and the other visitors. While not required, posted pictures are encouraged.
2) Do a little research on glaciers. Include a fun or interesting fact about Exit Glacier, the Harding Icefield, or glaciers in general in your log.
3) Along the paths, there are a number of signs bearing dates. These signs mark where the toe of the glacier was at that time. Waypoint as many of these signs as you can find and email me your results. DO NOT include these waypoints in your logs.
4) Using the waypointed dates, calculate the approximate rate of advance or retreat of the glacier. Is the glacier advancing or retreating? What is the fastest rate that you calculated? What was the slowest rate that you calculated? Email me your results. DO NOT include these results in your logs.

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Inventory

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132 Logged Visits

Found it 127     Write note 4     Publish Listing 1     

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Current Time:
Last Updated: on 10/13/2014 7:38:42 PM Pacific Daylight Time (2:38 AM GMT)
Rendered From:Unknown
Coordinates are in the WGS84 datum