During some mornings in Yosemite Valley, when streamflow is relatively high but temperatures are below freezing, some creeks may seem to be full of slush rather than full of water. This is frazil ice, which forms when mist (for example, from a waterfall) freezes, then floats down the creek.
When can I see frazil ice?
While working on Yosemite Nature Notes' Frazil Ice episode, the producer (Steven M. Bumgardner) noted how often frazil ice occurred on Yosemite Creek. In 2009, he witnessed about seven frazil ice events on Yosemite Creek, mostly in April. In 2010, there were 20 or 30 events in April, May, and even early June.
Where can I see frazil ice?
A similar form of frazil ice commonly occurs elsewhere in the US and Canada, for example, in the upper Midwest and along the Hudson River in upstate New York.
Did You Know?
The Merced River was designated a National Wild and Scenic River in 1987. Eighty-one miles of river runs through Yosemite National Park, including a stretch in Yosemite Valley.