Maps of a glacier made at two different points in time can be compared and the difference in glacier thickness observed used to determine the mass balance over a span of years.
(a glacier; made; L:at two different points; T:in time) (Maps of a glacier; can be compared; ) (the difference in glacier thickness; observed used; to determine the mass balance over a span of years)
a glacier Maps of a glacier the difference in glacier thickness
made can be compared observed used
L:at two different points T:in time
to determine the mass balance over a span of years