Ice, Ice, Maybe

There's an exceptional accumulation of waterfall slurry ice below Yosemite Falls right now, and the whole amphitheater is closed for safety reasons. The stream of 'frazil' flow meanders dynamically and it'd be possible for someone to get into real trouble with this unstable landscape. We know it's not really 'frazil ice' because this slurry is formed of frozen waterfall mist/droplets, but it's remarkable, whatever we call it.

There's frazil deposition in Royal Arch Creek and Steve B. says there's frazil in Bridalveil and Ribbon Creeks.

There's also a very healthy snowpack at higher elevations, well above average in depth and water content. The Valley has lots of water from recent storms; there's almost a foot of snow on the ground but running water in Sentinel, Eagle, Royal Arch, Ribbon and other creeks. This wet winter bodes well for summertime waterfalls, some groundwater recharge, and perhaps a more normally-timed start to the fire season. We'll have to wait a few months to fully assess the end of the drought.

Meanwhile at lower elevations flowers are blooming in the Merced River canyon: fiddleneck, baby blue eyes, and a galaxy of waterfall buttercups can be found.

Into Merced Grove

After weeks of nice foliage color, it's STILL really colorful in Yosemite. Black oaks in the Valley have come into their own, dogwoods, bracken, azalea, dogbane and maples are still so bright. Adding to the glow, now the forest floor is lightened by fallen leaves, too. I was with a group in Merced Grove over the weekend and we enjoyed the quiet of the big trees enhanced by the startling albedo change brought on by yellow dogwood, azalea and hazel. What a colorful look for this deep shady valley.
It was mighty pleasant to walk on the old Coulterville Road to the old ranger cabin, in the middle of Yosemite's smallest sequoia stand. I'll be snowshoeing in for a night in the ranger cabin with another group the first weekend of February.
Sunday night brought snow down to about 6000' in Yosemite. Glacier Point Road and Tioga Road are closed, perhaps for the whole winter now. The Valley's great fall colors now include a good amount of white, from snow extending down from the south rim, and ice that builds on Yosemite and Sentinel Falls.

Yosemite's Curious Frazil Ice

2 April 2010

This is the month when locals look for frazil ice flows in Yosemite Valley. They can occur below any of our waterfalls, but are most often seen on large scale below Lower Yosemite Falls, when deposits can cover acres with what looks like snow, and can persist for months. We've had frazil forming on several recent mornings in Bridalveil and Yosemite Creeks.

It's hard to describe this material and its origin if you haven't seen it for yourself. Look at http://www.nps.gov/yose/photosmultimedia/ynn.htm in May for an NPS video that'll give you an idea. Imagine a creek turned into a slurry of suspended ice particles, or a lava flow made of ice, or spilling a million-gallon slushie drink into the forest.

It forms mostly in the spring when warm temperatures melt snow into high run-off and lots of mist in the waterfalls, then overnight freezing temperatures turn a portion of the spray into ice droplets, which flow along in the full creek. Because we get these conditions regularly, Yosemite is one of the best places to observe this 'waterfall spray ice' being created and then slowly melted away. There's a persistent myth that these deposits represent the sudden collapse of the Upper Yosemite Falls snow cone (a huge mound of ice that accumulates below the falls), but this is emphatically not the case. Frazil flows happen when it's quite cold, beneath falls with no snow cones, and they can happen repeatedly for weeks.

If you're lucky enough to be in the park this month, stroll by the base of the falls for a look.