Alaska's glaciers are constantly on the move, but every so often they put on a show that reminds us just how alive these frozen giants really are. In a both mind-blowing and terrifying new video from Kenai Fjords National Park, a massive avalanche of snow and ice is captured cascading down the face of a towering glacier before crashing into the ocean below. The impact sends a series of powerful waves racing across the fjord, while a cloud of ice and spray erupts into the air. Unlike the classic glacier calving events that have become famed among adventure novelty-wave surfers, this wasn't a massive slab of ice breaking cleanly from the glacier's face. Instead, it was a full-blown avalanche, with countless tons of snow and ice tumbling down the steep mountainside before slamming into the water all at once. View this post on Instagram The result is every bit as mesmerizing.…