Frazil ice flows are dramatic natural events that occur in the waterfalls of Yosemite Valley during March and April. I had never heard of Frazil Ice until I saw this cool video and sat mesmerized as I learned about this unique event that occurs in Yosemite National Park. Be sure to watch Yosemite HD Time Lapse. If you are planning a visit to Yosemite consider springtime and avoid the summer crowds.