Thursday, February 7, 2008
'Snow Use: PolyChromatic Geology (2-phase Geothermal Contrasts)
Sullivan's Knoll is a young (10k + years) Cone and Crater (breached), which sits atop or near Ivin's Knoll of 100k+ years basalt flow.
Snow on the Slopes!
A white covering on the ground surface allows an inspection of possible warm spots near WA County’s dormant volcanoes. After watching Mt. Baker (an active vent for the San Juan de Fuca subduction there) to the north of my Snowbird home in Washington State, I realized that there was a method of finding geothermally warm patches of earth independent of using expensive equipment. Every summer, I notice that there is a large area which always darkens before the rest of the mountain. The recent snow in WA County allows a similar test of Sullivan Knoll near my winter residence.
Sullivan’s Knoll is a Crater and Dome which has an age indicated by Erosion of ~ 10k years+. Cracks in driveways oriented towards the present crater and de-gasification is occurring increasingly (possibly due to leveling on the flanks by present developers).
Sullivan's Knoll appears considerably different after a snowstorm- we're searching for a warm spot (I haven't found one)!
The craters and domes in the City of Hurricane are not active, and Utah Geology Survey measurements indicate an age generally in excess of 100k years. However, dating may not be used for young ash and porous ejected rock. In this case, radioactivity used for the measurements from Argon gas is unreliable. Erosion is one method of approximating the ages, and that is the source of the 10k year for the youngest cone. After observing old cones and craters in AZ, HI, NM, and WA, I find that one can estimate the age of last eruption by looking at crater erosion, allowing for the climate of the region.
Hurricane West Crater is older than Sullivan’s Knoll (100k+ compared to 10k+ years), but SK base rests on a previous basalt emission from Ivin’s Knoll which is somewhat older than HWC.
This Crater may be accessed across "Turtle Preserve" lands just north of 600 N, near Gould's Wash.
When a scan is made of basaltic volcano age for the Colorado Plateau, CP, there is a gradual movement of volcanism from the Rio Grande Rift at about 40 mybp, to the St., George area at the 1 mybp date (now, in geological terms).
This basaltic eruption has moved westward around the south edge of the CP in a regular manner. This cannot be due to radioactive heat, since the oldest heat-emitting radioactive compounds have been shoved under the CP on the west edge first (during the Laramide episode). If anything, heat from subducted elements, such as K, Th, and Uranium, would build up on the west side of CP and move eastward with time.
The first possibility that comes to mind for this dilemma is that of density change, where a Physical-Chemical rule for a three factor system has a solution. Whenever the 3 factor system is that of c, composition, T, temperature, and p, pressure (pTc), the rule finds that if a fluid is compressed by depth or pressure, the mass will tend to change density to offset the increased pressure. When this happens, the composition will change to accommodate the system. For example, whenever one pressures an auto tire, the density increases, and the rule states that there will be an attempt to maintain the previous lower density by increasing the temperature. (the tire gets noticeably hot). Oppositely, whenever the air is let out of the tire, the air becomes colder. "Rounding up the Usual Suspects" of Basalt- converting to higher density eclogite- could release Heat, similarly to the compressed AutoTire when it is compressed sufficiently. There are other possibilities, such as Granite converting to Feldsite, but Basalt is the most commom heavy rock which subducts into the Mantle.
A Hogback is developing, as we speak, due to cooling of the Magma near the Hurriane Cliffs (deep below) and its shrinkage more at the face of the Cliffs where the heat can ecape more readily.
For the case of subduction, since the basalt was shoved under the crust earlier on the west side of CP (Laramide episode), the heat from a change of basalt towards eclogite will generate heat lastly, since the depth (p) is less there than on the east side (Rio Grande area). Heat will develop first at the Rift, since the basalt is deeper there. Shallower emplacement near ST. George, UT causes later buildup of heat to the west, since the rate of change of composition is less for the lesser depth (if you pressure the tire slowly, heat will not be as noticeable). The heat of conversion of basalt to eclogite remains, but is slower to develop as a magma.
Notice the Flat and Level Beds East of Hf, compared to Turmoil to the west- this is correlated with the movement of vulcanism clockwise around the CP from the Rio Grande Rift (starting at about 40 mybp until 1 million years ago)
Stout Park Crater, SPC, remains higher in elevation, possibly because it is younger than West Crater, HWC. On the east side of SPC, as well as dominantly on SPC, there is red ash