Depositional Features of Glaciers

Depositional Features –soft sediment left behind by glaciers, formed by retreat

• Unsorted - direct contact with ice

• stratified (layering) - meltwater organizes sediment.

Outwash (167) - broad accumulation of stratified drift adjacent to end moraine

• meltwater from retreating glaciers drop a load of stratified drift

• smooth plains of sorted sand material from braided streams of glacial meltwater carrying material ground up

• when confined to mountain valley, is called a valley train

Till (Ground moraine) (165) - leftover sediment from retreat of glacier

• material dragged along the bottom of the glacier. 

• Poorly sorted

• levels ground, filling in low spots

Moraine (165) - layers/ridges of till

• Lateral - accumulation of debris along sides of valley - (valley)

• Medial - two glaciers coalesce, and lateral moraine join to create dark stripe of debris - (valley)

• End (terminal) moraine - (either valley or ice sheet)

  • most helpful 

  • form at snout of glacier, if glacier is steady (in balance) for a long period of time. 

  • The longer the glacier is in equilibrium, the larger the end moraine - from inflow of debris.

  • Marks where the glacier last stood.

  • Multiple can form if the glacier retears and stabilizes again (recessional end moraines). The first one to form marks the farthest advance of the glacier

• Ground - till, leftover debris from glacier melting - (either valley or ice sheet)

Drumlin (168) - asymmetrical hill of till

• can be used to determine direction of glacier:

  • steep - where the glacier came from

  • gentle - where the glacier was advancing

• material bulldozes into a mound 

• teardrop shape

• made of till and sediment. 

• will carve striations into rock and cause abrasion. 

• not to be confused with roche moutonnee

Kettle Lake (167) - lakes formed from ice taking up space in the ground, and then melting leaving a depression.

• large/small lake in soft material

• blocks of ice that are buried into the ground, melt creating pits in sediment

• ex. Walden Pond

Presumpscot formation (Boston Blue clay)

• forms where land has been depressed and pushed downwards, and weight of glaciers pushes land sometimes below sea level, and fine stuff in glaciers will settle out in ocean water. leftover creates clay

Erratic (164) - boulders that don’t represent bedrock

• random boulders that don't match bedrock below

• can be frozen at bottom of glacier: 

  • on top = angular 

• bottom = striated

• can be used to trace the path of an ice lobe.

• can be found on farms and pastures

Esker (168) - ice tunnels

• ridges made completely out of sand and gravel

• created through streams in tunnels underneath the ice

Kames (168) - asymmetrical mounds or hills

• composed of sand and gravel

• created from sediment washed into depressions in the wasting terminus