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Wednesday, January 11, 2012

What is Happening with the Spring Temperatures ...

The spring sources that feed the two pools at Scenic Hot Springs typically run hot throughout the winter months.  However, in the springtime as the melting snow-pack accelerates, ground-waters mix with the source of the Lobster Pot feed, dropping it's temperature radically and increasing the water flow several times.  Normally this happens much later in the season, however, the recent higher temperatures in the passes have melted a lot of snow into the ground water near the spring sources.

The two main hot spring sources at the main pools are the Lobster Pot feeds (for the normally hotter pool) and the Bear Den feeds (for the other pool).   These two sources are completely different . . . undertaking separate routes from the hot rock 600ft below to the surface.    Lobster Pot emerges shallow in a natural depression  overlain with a thick, subsurface band of decomposed, friable granite.

Decomposed (or altered) Granite.  The grains lose coherence because of
the leaching of feldspar by water.  More resistant minerals remain in a
friable matrix open to easy infiltration by ground water.  The brown color is
due to the release of iron oxide.

This friable granite layer (very visible lower on the trail near Honeymoon Springs) overlays much of the bedrock in the area.  Thousands of years of ground-water flows have leached the softer feldspar out of the granitic bedrock, leaving behind loosely-held quartz . . . a ready-made channel for surface waters to percolate through.

Anyone who has spent some time soaking up at Scenic will probably have noticed the appreciable amount of tiny rock-like granules discharged at the end of the feed tube into the hotter pool (the one fed by the Lobster Pot feeds), while the feeds from Bear Den hardly deposit much more than a small amount of silt to the bottom of the pool.  The Lobster Pot sources are travelling shallowly within decomposed granite and picking up some of those granite grains (the precursors to sand by the time these waters make it to the lowlands) before emerging to the surface.

Looking down the soil bench near the sources for Lobster Pot
(the feed pipe can just be seen in the upper right).  The soil here is
exposed decomposed granite within an ancient watercourse.

The feeds for Bear Den are on the other side of the large boulder
to the left, in a depression of firm bedrock covered by a light layer
of clayish-soil devoid of decomposed granite.
Lobster Pot thus becomes much more susceptible to mixing with ground water that is is channeled into that ancient water course during the annual snow-melt (and at times of heavy rainfall).  Once the melt is over and the upper layers of decomposed granite transition to an unsaturated state, the springs return to their normal temperature levels.

Decomposed (aka Rotten Granite) has almost completely filled
an abandoned pool lower on the property in an area we call
Meadows Springs.  As you may note, the spring waters flow
easily through this material.  These lower spring sources are
off-limits because of the fragile and unsteady nature
of the slopes they are within.

Hopefully, in early-season melts like this, we would expect that winter is not quite over with yet and a cold snap of sufficient duration would re-freeze that shallowly traveling melt and lock it up . . . allowing Lobster Pot to resume it's normal temperatures.  Colder weather is expected later this week . . . hopefully enough to abate this temporary dip in the temperatures of the hotter feed.

Bear Den, in contrast, emerges from bedrock without an overlaying band of porous, decomposed granite.  The Bear Den feeds are much more resistant to changes in feed temperatures and even during the height of the snow-melt will remain constant.

Visitors to the hot springs should keep this in mind when they request permission.  There is no way to predict with any accuracy when rain or melt will affect the temperatures of the springs.  Lobster Pot will run cold while there is an abundance of rain or melt saturation in the ground . . . and recover just as quickly once that source of mixing has dried up.  Bear Den will happily ignore these cycles and just go on pumping out nicely-soak-able hot spring waters . . .   When we identify such situations, we limit the number of reservations allowable each day for the remaining usable pool.

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