As a glacier flows downhill, the weight and pressures of the ice tend to "flatten" or broaden the valley -- hence, it creates the characteristic U-shape.
(a glacier; flows; downhill) (the weight and pressures of the ice; to flatten; ) (the weight and pressures of the ice; to broaden; the valley) (it; creates; the characteristic) Context(it creates,List([115, 125))):(the weight and pressures of the ice; tend; to "flatten" or broaden the valley)
it creates,List([115, 125))
a glacier the weight and pressures of the ice the weight and pressures of the ice it the weight and pressures of the ice
flows to flatten to broaden creates tend
downhill
the valley
the characteristic
to "flatten" or broaden the valley