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Martha Lake Airport Park Erratic EarthCache

Hidden : 2/13/2017
Difficulty:
1 out of 5
Terrain:
1.5 out of 5

Size: Size:   other (other)

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Geocache Description:

Welcome to Martha Lake Airport Park. The coordinates lead you to an information board about a glacier erratic block, locally known as "Big Rock". Big Rock is one of the largest glacial erratic boulders in urban King, Snohomish, and Pierce counties. The retreating ice sheet dropped this massive rock at its current location about 12,000 years ago. Big Rock is also a popular Bouldering rock. (Bouldering is a form of rock climbing that is performed without the use of ropes or harnesses.)

Answer the following questions:
  1. In your opinion, how has the surrounding area been affected by retreating glaciers?
  2. What glacier eroding process left "Big Rock" where it is today?

A glacial erratic is a piece of rock that differs from the size and type of rock native to the area in which it rests. "Erratics" take their name from the Latin word errare (to wander), and are carried by glacial ice, often over distances of hundreds of miles. Erratics can range in size from pebbles to large boulders.

In geology, an erratic is material moved by geologic forces from one location to another by a glacier. Erratics are formed by glacial ice erosion resulting from the movement of ice. Glaciers erode by multiple processes:
  • abrasion/scouring
  • plucking
  • ice thrusting
  • glacially-induced spalling

Glaciers crack pieces of bedrock off in the process of plucking, producing the larger erratics.

In an abrasion process, debris in the basal ice scrapes along the bed, polishing and gouging the underlying rocks, similar to sandpaper on wood, producing smaller glacial till.

In ice thrusting, the glacier freezes to its bed, then as it surges forward, it moves large sheets of frozen sediment at the base along with the glacier.

Glacially-induced spalling occurs when ice lens formation with the rocks below the glacier spall off layers of rock, providing smaller debris which is ground into the glacial basal material to become till.

While you are here enjoy all other features the park has to offer

  • Skate park
  • Picnic shelter
  • Soft ball field
  • Tribute statues
  • Play ground
  • Walking paths
  • Restroom facilities

To log this cache, you must email me the answer to the questions, do not include the answers to the questions in your "Found It" comment logs.

including a picture of yourself or your party on your "found it" log is optional, but encouraged. Extra points if your picture is from the top of Big Rock.

you don't need a reply from me to log this cache, but logs without email be deleted.

Additional Hints (No hints available.)