Glacial deposition landforms - Moraines

Glacial deposition landforms - Moraines

1. Lateral moraines

   • Ridge of till running along edge of glacial valley, orientated parallel to direction of ice flow
   • Example at Athabasca Glacier 1.5km long and 124m high
   • Material which has been frost shattered from the exposed valley sides above the level of ice, falls onto the sides of the glacier by rockfall and accumulates on top of ice.
     • As glacier retreats the material is gradually lowered and deposited on ground at sides of valley.

2. Medial moraine

   • Found on the floor of previously glacial valley. These features are aligned with the direction of ice movement
   • Length 1-20km width 50-100m
   • Formed where two glaciers meet where the lateral moraines (debris on edges) of two adjacent valley sides converge and is then carried on top of middle of enlarged glacier.
   • Consists of angular and poorly sorted materials.

3. Terminal moraines

   • A ridge of material stretching across glacial valley at the farthest extent of the ice
   • Elongated at right angles to direction of ice advance. Usually steep sided, particularly ice contact side
   • Angular and poorly sorted material
   • Width 20-500m
   • Often crescent shaped, moulded to form of snout
   • Crescent shape due to position of snout- the centre of glacier advances further as friction with the valley side causes more rapid melting at the sides.
     • Steeper up-valley side is result of the behind supporting deposits making them less likely to collapse

4. Recessional moraines

   • Series of ridges of material that are parallel to each other and to the terminal moraine, found up valley of the terminal moraine. Rarely greater than 100m in height
   • Form during standstill in glacier's retreat when material is deposited in front of re-positioned snout.
     • Size of the ridge is dependent on the pause of the glacier.
       • For significant ridges to develop there needs to be long pause in glacier movement, hence seldom greater than 100m

5. Push moraine

   • Same outward appearance as terminal or recessional moraine but stones in till tilted upwards
   • Formed during ice advancement, pushing previous moraine deposits such as terminal/recessional moraines forward in front of snout and pushes stones up
   • Faster the advance, the greater the angle of tilt of the orientation of the stones