Dozer operator was shoving coal into a reclaim feeder. Employee's dozer slid into a cavity. The dozer slid toward the feeder with the blade up. The operator notified the plant operator. A dozer and a backhoe removed enough coal for the operator to exit the dozer. Employee was in the dozer for around 70 minutes. The event was phoned into both WVMHS&T and MSHA.