Ice Age EarthCache
Hidden : 11/16/2014
Difficulty:
1.5 out of 5
Terrain:
3.5 out of 5

Size: Size: large (large)

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Geocache Description:

This cache is along the trail leading up to Oyster Dome.

If you park on Blanchard Mountain a Discovery Pass is required. No pass is required if you start from Chuckanut Drive.

GLACIERS
The movement of a glacier is due to the properties of ice. Under tremendous pressure, there is a change in the crystal structure of ice, and it will flow, both by melting and refreezing; and then sliding of one crystal past another. Glaciers will flow when greater than 200 feet in thickness. The rate of flow will depend on the pressure behind the ice, and the steepness of the downward slope.


Think of Puget Sound as a water-filled valley between the Olympic and Cascade Mountains, carved by powerful glaciers that advanced and retreated during four different Ice Ages stretching back hundreds of thousands of years.

During those formative years measured in geologic time, the land mass that now is home to more than 3.6 million people was buried under ice over 1 mile thick. Puget Sound, as we know it today, was formed about 13,000 years ago at the end of the last Ice Age when an ice dam across the Strait of Juan de Fuca broke loose, allowing the marine waters of the Pacific Ocean to rush into Puget Sound and mix with the waters from the two mountain ranges to form the treasured body of water named by British explorer Captain George Vancouver in 1792.

Continental ice sheets have repeatedly advanced and retreated from the Puget Sound region. The most recent glacial period, called the Fraser Glaciation, had three phases, or stades. During the third, or Vashon Glaciation, a lobe of the Cordilleran Ice Sheet, called the Puget Lobe, spread south about 15,000 years ago, covering the Puget Sound region with an ice sheet about 3,000 feet thick near Seattle, and nearly 6,000 feet thick at the present Canada-US border.



Since each new advance and retreat of ice erodes away much of the evidence of previous ice ages, the most recent Vashon phase has left the clearest imprint on the land. About 14,000 years ago the ice began to retreat. By 11,000 years ago it survived only north of the Canadian border.

In the Puget Lowlands, the Puget Lobe shaped much of the topography below 3,000 feet. The ice sheet had exerted enormous pressure, pushing the land down, but over time the land rebounded. Puget Sound at one time was 300 feet below its current sea level due to the land rebounding from lost glacier melt.


As glaciers advanced and retreated, melting ice created streams and lakes. A massive melt water lake formed and swelled 120 feet above today's Puget Sound. As the glaciers advanced and retreated they carried silt, rocks and boulders. These materials were often pressed into the bedrock and left striations, grooves, and other markings. These markings often indicated the movement of the glacier. Evidence of this process is visible at the posted coordinates.

REQUIREMENTS:
Please log your find and then email answers to the questions below in a timely manner.

At the posted coordinates:
1) How much ice covered the posted coordinates? (read the EarthCache page)
2) Is the rock you are standing on a soft sandstone type rock or a harder quartzite type rock?
3) What color is the rock?
4) Estimate the dimensions of the rock formation at the given coordinates (height, width, and length in feet or meters).
5) How deep are the striations? (in inches or centimeters)
6) Describe the view while looking westward from the EarthCache area.

REFERENCES:
- Special Report by The Olympian on 6 Aug 2006
- Wikipedia reference to Puget Sound geology
- HistoryLink.org Essay 5087 Department of Ecology: Puget Sound Shorelines Glacial Geology of the Puget Lowland, Dale W. Cole (1967 unpublished class handout)

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