Definitions for upthrustˈʌpˌθrʌst
Random House Webster's College Dictionary
a thrust in an upward direction.
Geol. an upheaval of a part of the earth's crust.
Origin of upthrust:
upheaval, uplift, upthrow, upthrust(noun)
(geology) a rise of land to a higher elevation (as in the process of mountain building)
an upward thrust
an upward movement of part of the Earth's crust
to thrust something upwards
to be thrust upwards