In order to complete this EarthCache you will need a thermometer and to complete some calculations.
For those of you that forgot a thermometer, you can find one in the nearby cache cleverly named "The Thermometer". Just be sure to put it back before you leave.
Parking is located in a small dirt parking lot near the 101 and 1. A parking fee is required if using that lot, though an additional 0.25 mile walk will get you parking on the street. The short but uphill hike is mostly along a fire road, but the last couple hundred feet is a single track overgrown with grass, berries, poison oak.
The Las Cruces Hot Spring in Gaviota State Park is located along the South Branch Santa Ynez Fault. The Santa Ynez Fault is a major fault that extends east along the Santa Ynez Mountains east past Ventura. The fault is a nearly vertical reverse fault that has been involved in the formation of the Santa Ynez Mountain Range.
The fault likely acts as a conduit for groundwater that has been heated deep in the ground to find its way to the surface. Water percolates down through the ground and warms up. Then at this spot, either from pressure, temperature differences, dissolved gasses, the water is pushed up along the fault reaching the surface.
The water brings dissolved gasses to the surface as well. At depth, the water is under a lot of pressure, so a variety of gasses become dissolved in it. At atmospheric pressure, those gasses come out of solution forming bubbles. These bubbles can be seen and smelled from a number of spots in the spring.
In addition to the gasses various chemicals are dissolved in the hot water. The La Cruces Hot Springs has an elevated concentration of fluoride.
In this area the temperature of the rocks is estimated to increase by 25ºC every kilometer. By using the temperature of the water coming out of the spring geologists have estimated the depth below the ground from which the water has come up along the fault. Their estimate is 2.9 kilometers.
Using your measurement of the temperature of the hot springs from the furthest upslope pool (a small 2 foot diameter pool at what appears to be the start of the spring) and some very simplifying assumptions you will calculate the source depth of the spring. A couple of those assumptions are that the water does not cool on its way up, the temperature gradient is constant, and the average surface temperature of the area is 18ºC.
Logging requirements:
Send me a note with:
- The text "GC58GDX Las Cruces Hot Springs" on the first line
- The number of people in your group (put in the log as well).
- What is the temperature of the water in the pool at the start of the spring?
- What is the depth of the source of the spring? Figure this out using the following formula to figure out the depth in kilometers. Be sure to convert your temperature to Centigrade.
((Measured Temperature)-(Average Surface Temperature))
25
- If your depth does not match, guess as to why not?
The following sources were used to generate this cache:
- Miller and Rapp. 1968. Reconnaissance of the Ground-Water Resources of Ellwood-Gaviota Area, Santa Barbara County, California. United State Geological Survey. Open File Report 68-182. April 10.
- Kharaka, et al. 1999. Geochemistry and Hydromechanical Interactions of Fluids Associated With the San Andreas Fault System, California. Faults and Subsurface Fluid Flow in the Shallow Crust. Geophysical Monograph 113. American Geophysical Union