Weather was marginal the day I flew into northwest Alaska's Glacial Lake ceilings-seven hundred feet and ten miles. The lake was dead calm. Glassy water confuses a pilots depth perception, risking the possibility of touching down before he expects, or after. In either case, it could spell catastrophe. With pitch attitude and power preset for a 100 fpm rate of descent, I let the floatplane gently settle onto the glassy surface. Suddenly, wham The Cessna 180 lurched violently to the right. I saw a large portion of the right pontoon break away and violently rip into the fragile underside of the starboard wing above. The airplane crabbed hard to the right. Then, as if in slow motion, the left float assembly collapsed under the excessive load, dipping the portside wing straight into the water-it buckled like a straw. As suddenly as it happened, it was over. In one terrifying moment I realized the cockpit was rapidly filling with water. Clawing at the seat belt, I got it loose, only to realize the door would not open. Frantically, I repeatedly smashed my shoulder against it. The aircraft was sinking fast, and only moments before, it would disappear forever into the deep, dark abyss that had captured it. I silently escaped into the freezing, glacier water.