Formation of Eskers REAL

Question 1

Part 1

Answer 1

• An esker is long, sinuous ridge composed of stratified sand and gravel laid down by glacial meltwater. Material is deposited in sub-glacial tunnels as the supply of meltwater decreases at the end of the glacial period.
• Sub-glacial streams may carry huge amounts of debris under pressure in confined tunnels at the base of the glacier.
• Some scientists argue that deposition occurs when the pressure is released and meltwater emerges at the glacier snout.

Question 2

Part 2

Answer 2

• As the glacier snout retreats, the point of deposition will gradually move backwards.
• This may explain why some eskers are beaded - the ridge showing significant variations in height and width - with the beads of greater size representing periods when the rate of retreat slowed or halted.
• However, others argue that the beads are simply the result of the greater load carried by summer meltwater (Figure 2.24).
• The Trim esker near Dublin is one of a group of twelve in the area.
  It is 14.5 km long and between 4 and 15 m high.