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Glacial Striations

Schoolyard
Geologist in ACTION
Broom Striations
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Location: Emerson School Playground, Berkeley, California
About: If you look carefully at the ground, you can see a bunch of parallel lines. These formed when workers used brooms to distribute the tar of the blacktop evenly over the playground surface. The lines are a permanent record of the abrasion and scraping of the broom.
Glacial Striations Outcrop
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Location: Glacier National Park, Montana
About: Glacial "striations" on bedrock. Rocks embedded in the bottom of a massive glacier scratched the rock underneath as the glacier moved along. Even though there is no ice present today, these scratched lines are evidence that glaciers were here in the geologic past. We can even tell which direction the glacier was moving by the direction that the lines point!
Asphault 'flow'
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Location: Emerson School Playground, Berkeley, California
About:

A close-up of more broom-marks on a concrete walkway.
Closeup of Glacial Striations
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Location: Isle Royale National Park, Michigan
About: Glacial striations are parallel to the handle of the hammer. Look at how the lines all go the same direction.

Worker pushing broom

Bulldozer

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About: The scratch marks on the schoolyard are formed by the process shown on top -- a broom dragged along over wet tar. You can imagine similar scratch marks from a bulldozer pushing rocks.
Exit Glacier, Alaska
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Copyright Marli Miller, University of Oregon

Location: Exit Glacier, Alaska
About:

A massive glacier slides downhill, pushing rocks out of its way like a bulldozer as it goes. When it eventually melts, there will be scratch marks left behind underneath it.

Key Concepts:
  • Glaciers are made of ice and rocks that get trapped in the ice.
  • Glaciers flow downhill because of gravity.
  • The moving glacier acts a lot like a bulldozer, stripping away layers of rock and moving them off to the side.
  • Rocks embedded in the bottom of the glacier scrape along the newly exposed bedrock and leave behind line-shaped scratch marks. (We call these "glacial striations").
  • The direction of the scratch marks tells us the direction that the glacier flowed.
Links for further Exploration:

USGS Water Science for Schools - Glaciers and Icecaps

Glacier Image Library Very detailed, well organized, high quality images of glaciers.

Glaciers and Glacier Features
Classroom Activities:

Glacial Scratching [Middle School] Students make mini-glaciers and use them to make scratch-marks on a piece of wood.

Web Quest 1 [Middle School]
Web Quest 2 [Middle-High School]

Schoolyard Geology Home  •  Lesson 1  •  Lesson 2  •  Lesson 3  •  Downloads

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Page Last Modified: Wednesday, 12-Dec-2012 15:07:24 EST