Which of the following causes basal sliding of glaciers?

W) Melting of basal ice due to heat from friction as the glacier moves along bedrock

X) Changes in gravity as the glacier increases in mass

Y) Differences in the amount of friction linked to variable surface conditions under the glacier

Z) Decrease in friction due to melting from pressure of overlying ice
Z) DECREASE IN FRACTION DUE TO MELTING FROM PRESSURE OF OVERLYING ICE