Thursday, June 29, 2017

A solstice to remember

Our remarkable year continues to surprise with storms into June. The Merced River has hovered near flood level for several weeks, running 3-5 times usual volume. Only now is it showing a typical seasonal decline, more than a month later than 'normal.' Low elevation tributaries are already drying or dried, but the main stem still runs strongly.

The lower canyon shows an interesting color reversal of early spring's redbuds underlain by white Nemophila or Claytonia, whereas now it's the white of buckeye overlying the purple of Clarkia.

Steve's newest Yosemite Nature Notes video has been released; you can learn something about Yosemite's grizzly bears here. How would your Yosemite visit be different with grizzlies around? Here's a brief travel item on Yosemite in the Huffington Post. Both of these media items have something in common with this blog...

Tioga Pass opens to cars today, but don't expect any services in Tuolumne to open soon. Likewise, hiking will be quite challenging for a while because of lingering snow and high runoff. (Do not take chances with stream crossings!) This IS an exceptional year and we won't see the high country we've become used to.

Monday, April 3, 2017

Post-winter Recovery

Springtime is making its way uphill in the Sierra with redbud peaking in El Portal now while unfathomable snow persists above 7000 feet. It can hardly be said enough: WHAT a winter we've had here! Storms were repeated with good frequency and lots of Pacific moisture, leaving us with a tremendous snowpack. The snowline was a bit higher than historical averages; not much accumulated in Yosemite Valley (though we had lots of rain runoff), but higher elevations have had fantastical quantities. The central Sierra has 175% of usual water content in the current snowpack. Picture the meadows and forests in the May Lake area buried by 6-7 feet of water (not 6' of snow, but 6' of standing water) - that's the nature of how much mature, dense snow is covering the tens of thousands of acres of Yosemite's upper elevations.

<-Bridalveil in flood.

Storm damage has been considerable in/near the park, with Hwy. 41 having been closed for a month by a washout, and crews working hard to repair slope movement on the Big Oak Flat Road below Crane Flat in hopes of getting it re-opened before Memorial Day. Trails at and above the Yosemite Valley level have a lot of downed trees; trail crew sawyers will be very busy for much of the summer to get those cleared. When you visit the Valley, check out the fragments of bark-less logs below Bridalveil or Yosemite Falls from trees that were uprooted and thrown over the falls this winter. Since December there's been a huge deposit of frazil (wist) ice below Yosemite Falls, and we're now in the month when one is most likely to be able to observe wist ice flowing.

The excitement isn't over. Because of the closure of the Big Oak Flat Road, Hwy. 140 has been handling much more traffic. This past Saturday, visitors were waiting over 2 hours in a 3.5 mile-long line of 800+ cars just to get through the stoplight at the Ferguson rockslide detour west of the park. (Easily avoided by coming in before 9am on weekends.) Because of the road construction in the Valley, the main parking at Yosemite Village will be closed for the next two months, and detours are confusing to both new and veteran visitors. It's going to be a very nice improvement once it's completed, but parking and navigating can be challenges on spring weekends now. Half Dome Village and the new lot by Camp Four are best bets. The road crew is already working to clear Glacier Point Road.

But, wait, there's more. The Merced is running almost 4x average flow today. All that snow in the high country seems likely to bring us some degree of 'high water incident' between now and mid-June (sure to cover some Valley trails at least), depending on how the warming progresses. Yosemite explorers should expect a delayed start to summer, with Tioga Road opening late, trails covered by snow and fallen trees, and creeks difficult to cross.

Saturday, January 28, 2017

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.

Saturday, January 7, 2017

High Water 2017

I am quite impressed with NPS preparations for anticipated flooding in the next couple of days; this is much different from the surprises of 1997's flood. Forecasting has been honed and there's institutional memory of the last big one.

As of last evening, all visitors have been evacuated from the Valley. Staff housing in the Half Dome Village area has been evacuated and all other locals are being told to stay put as of tonight. Peak flow is expected late in the day on Sunday. Projections are for about 17,000 cfs at Pohono Bridge, where the Merced exits the Valley. Average river flow for this time of year is about 100 cfs, and because of this week's rain the river is carrying 572 cfs right now. Again, that projection is for the river to increase to 30 times the current flow by tomorrow evening. We had a flood warning in mid-December but the river didn't quite reach 5000 cfs; it needs to get to about 7000 cfs before the water comes up on to a road in the Valley. The river would first gently back up on to pavement at Wosky Pond on Northside Drive.

If we do get to 17,000, this'd make it the 6th biggest recorded volume for the Pohono gauging station. The bigger events were the floods of 1937, 1950, 1955, 1964 and 1997. Five 'big' floods in a century averages to every other decade or so. What some locals parochially call 'The Flood' of twenty years ago was only a little bit bigger than those other four were, and such floods affect far more than just Yosemite. There was no gauging station in 1862, when the Merced surely exceeded its 1997 size in a mega-flood that wrecked the whole state.

All these high water events happen December-February and are due to warm storms, which bring rain to high elevation instead of snow. There's a persistent myth that the 1997 flood was due to rain melting recent snows, but the science says that rain doesn't melt very much snow. The floods happen simply by high snowline causing tens of thousands more acres of watershed to receive rain. Especially in higher terrain with thinner soils and vast expanses of bare granite, that rain just runs off right away and swells the rivers downstream.

I share Muir's enthusiasm for such events; he witnessed and wrote about the flood of December 1871. While I shelter in place, I look forward to seeing the video record collected by the professionals.

Thursday, November 10, 2016

Vote every day

Yosemite did not notice that there was an election this week. The falls kept pouring, leaves continued to drop, critters went about their business with no regard for what we think is important. New green grass brightens the Valley and El Portal, as our growing season commences. Half Dome looks virtually the same as it did when Washington was president.

October turned into quite a wet month. Yosemite Falls came roaring back to life in the most marked transition that I've observed - from months of absence to May-caliber runoff volume. We had two 2-year storms within a week, the river went from less than 20 cfs to going above 3000 cfs twice; it's since dropped a lot, but is still more full than average. High country roads were closed by snow but have since re-opened in a stretch of considerable warmth. A rockfall above Arch Rock closed Hwy. 140 for about 24 hours.

As Edward Abbey wrote, 'Nature may be indifferent to our love, but never unfaithful.' This sanctuary will always be here for us. What happens in D.C. is one thing but you can vote for Yosemite every day of the week by acting on your concerns for places like this. How you treat others, what work you do, what you do with your money and with your time, all make real differences for the world and the future. Vote often.

Friday, October 14, 2016

Spider Web Season

It's been a warm October so far, though we are entering a few stormy days. This is the time of year when spiders launch themselves into the air to disperse. From an exposed perch, some spiders release a streamer of thin silk until the wind picks up the silk and the spider. This is a way that a species can distribute itself to new terrain. Of course, the spiders can't steer their flight and many will be carried into inhospitable habitat. Warm daytime updrafts in our sunlit canyon will loft thousands of meters of spider silk up along the cliffs. If you shield your eyes from the sun you're certain to see streamers of spider silk sailing above; binoculars reveal these non-winged invertebrates hundreds or thousands of feet up. Arachnologists refer to this behavior as 'ballooning' but I prefer the term 'kiting' as the lengths of silk are more like kite tails. Sailing spiders form a part of the community of aerial plankton - that's a real term for the column of insects, spiders, and other things adrift in the skies. When updrafts swirl in canyon eddies, great clots of spider silk form in the sky. When lift ceases or the clumps become too heavy, they drop to the ground and we get a glimpse of this marvelous behavior of something that can't 'fly' but can soar. Spider silk clots show up well on pavement, but they're a little harder to pick out forests and meadows.

The sugar maple in Old Yosemite Village is at its peak color. Our native deciduous oaks, maples and especially dogbane are also colorful now. The Merced is below average at 18 cfs, but will be starting its annual rise tonight. We hope that Yosemite Falls will return to visible flow this weekend.

Sunday, September 25, 2016

Summer Adios

We had a rainy day in the Valley last week = the end of summer's endless blue skies. Park visitation is slowing down, and my overstuffed schedule is slowing enough to pick up these notes again; I should acknowledge that my field season is just not the time for me to have much desk time. Last year showed an increase in visitors and this year is up 20% over that; some say we'll reach 5 million visitors by year's end. The publicity around the NPS centennial and low gas prices are likely factors in the growth. The portion of European visitors seems to be up despite the poor exchange rate for them.

Bucks have lost their velvet. Dogwoods sport bright red berries. The river dropped to 30 cfs (and bumped up a bit from recent high country precip). There were hints of snow in/above Tuolumne. Indian hemp is turning its brightest yellow, but oaks, maples and cottonwoods are still green. Lower down, the poison oak is nearly bare now.

Lyell 'Glacier' continues to shrink away; last winter's roughly normal snowfall did not grow the ice much. Our bighorn sheep herds are doing well. The past 2+ weeks have shown a steady sequence of small, shallow earthquakes beneath the southern Clark Range. Our fire season has been minimal; one lightning fire started 12 June near Chilnualna Lake and has crept through only about 300 acres in 3 months- the kind of low-intensity fire we need more of.

Traffic flow in the Valley is exciting at the moment, with construction on the road and parking in the Yosemite Village day parking area. If you come for a visit between now and next spring, you'll find some disruptions to driving and parking, but the end result should be a nice improvement. Also in the spring, Mariposa Grove will reopen to the public - great changes are taking place there, too.