What was found
(CAN) SHORTLY AFTER TAKEOFF, FLIGHT EXPERIENCED A HSTA RUNAWAY. ACFT HAD JUST DEPARTED RUNWAY AND FLAPS WERE RETRACTED TO 0 DEGREES. AUTOPILOT DISENGAGED. TRIM SELECTION INPUT MADE. STABILIZER TRIM CONTINUED TO RUN & ASSOCIATED AURAL ALERT SOUNDED. IMMEDIATE ACTION CHECKLIST WAS COMPLETED, AS WAS QRH PROCEDURE. MODERATE CONTROL PULL FORCES WERE REQUIRED TO FLY ACFT AT 10,000 & 250 KNOTS. CREW USED ACARS SYSTEM TO CALCULATE A WEIGHT & BALANCE, & REDISTRIBUTED CABIN LOAD TO ALLEVIATE CONTROL FORCES. ICE ENCOUNTERED AT 10,000 FT & REQUIRED DESCENT TO 8,000 FT. EMERGENCY DECLARED. ACFT RETURNED. FLAPS SELECTED TO 20 DEGREES WHILE BETWEEN 8000 & 6000 FT. CONTROL FORCES WERE SIGNIFICANTLY LIGHTER ONCE FL