On August 10, 2001, about 1315 Alaska daylight time, a wheel-equipped Stinson 108-2 airplane, N8090K, received substantial damage while landing at an off-airport site on the Knik glacier, located about 25 miles southeast of Palmer, Alaska. The commercial pilot/operator and the three passengers were not injured. The flight departed Merrill Field, Anchorage, Alaska, about 1215. Visual meteorological conditions prevailed, and no flight plan was filed. During a telephone interview with the NTSB investigator-in-charge on August 10, the pilot related he was landing the airplane at a site on the glacier that he had landed at several times before. On the accident flight, he said the left main tire hit a rock which blew the tire, and damaged the landing gear fuselage support structure and the cabin door frame. The pilot said there were no preimpact mechanical problems with the airplane, and that he did not see the rock prior to impact.