Thursday, February 7, 2008
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
Tuesday, February 5, 2008
Lake Powell is shrinking rapidly, with our drought conditions- accelerated by Global Warming- Notice the High Bathtub Ring.
Our Striking Colors of Outcropping Rocks are due to the Highly Oxidized Sediments in the Mesozoic, as well as Desert conditions now (in Late Paleozoic time, the massive outpouring of Oxygen from vast new forests displaced the previous dominant CO2 atmosphere- moving CO2 into limestones).
Dry Arroyas offer the best chance to view Ancient Rock Formations, untrammelled by man (But not after Recent Rains)
Call to Hikers
Come take a walk with me today-
We’ll climb a high hill,
Sampling her creation along the way.
We’ll live in our mind’s eye awhile,
Seeing things she did so long ago.
The curt breeze will mask our bootsteps,
While we remember how it was in our childhood-
The collectible stones, the new valleys.
How fresh it all was!
We’ll see the young lavas,
How warm they were yesterday,
When our senses had no imprint of history.
How we laughed at the rocks sliding,
Rushing to cross our paths,
Long before there was such a thing as anxiety.
We’ll cross trickling streams,
If we’re lucky enough for spring rains-
Our hands will slap the cold waters,
Taking the place of bare slender feet.
We’ll love life- once again.
Harold L. Overton
Monday, February 4, 2008
Part of Hurricane Fault, Hf, can be Measured for Orientation near Hiway 9 east of Laverkin (notice the alignment of a saddle with the fracture direction)
A Monocline or Hogback has risen across the Virgin due to cooling of Subsurface Magma at the face of the Hurriane fault (as evidenced by open cracks on its east side and dropping house lots on the Laverkin cliffs to the East)
Google Photo above shows the Virgin River and its border between Hurricane and Laverkin
Hurricane (Stout) Park Volcano, SPC- S27 41S 13W, named Radio Tower Volcano, by UGS
Access to this hike is made in the Town of Hurricane, going north on 200 West street from Hiway 9, until the city park is reached on the west side (750 West). Turn left, or west, to the gravel road which runs along the boundary of the park, and drive to the end, about 200 yards. Park on the shoulder at the park corner (bounded by a fence corner). Cross a ditch and at the fence corner, enter the volcanic boulder-strewn pasture land. Use either the existing faint trail past the waste storage pond to the west, or hike through open sloping land on the volcanic skirt to the NW. Proceed to the top and walk along an old cattle road to the north rim of the crater. This is just above the Virgin River, where the countryside with all of its’ impressive views are presented. We will look down on the river, the Mesozoic rocks, and the young volcanic detritus toward the north and west.
Section 27 has a 100k+ year extrusion (old lava flow) with a slight crater remaining. Hike with an objective of overlooking the Virgin River at the crater rim, to see the shear cliffs of basalt from several flows and sedimentary rock. A great sweep of the Laramide Virgin anticline, lava flows, and young faulting can be evaluated from a single stance.
Stratigraphy west of Hurricane fault (Hf) is highly contorted, while remaining almost flat and level to the East
Try to focus on the following Features shown, looking to the north and NE:
1. The Hurricane Mesa (high plateau with towers on top) to the east- which has flat and almost level strata (beds of sediments, which are laid parallel to each other);
Hurricane Mesa is to the East (Right of Photo), and is almost flat and level, compared to formations west of it in the Transition Zone
2. Tilted pink-colored monocline or Hogback, just across the Virgin to the north;
3. Basalt flows into the Previous Virgin canyon, as shown by black rock higher in elevation than the present river bottom;
Notice that the Black Basalt has moved into all available crevices
4. Basalt rock which is irregular on the base and sides (indicating filling of old canyons and faults and fissures);
5. Pine Valley Mountains, PVM, to the north and NW- which are an intrusion of granite-like rock rising in the Miocene, about 21 million years ago; and
6. The Virgin Anticline between PVM and the Virgin, which were compressed upward in the Laramide Compression from the west about 100 m.y. ago (notice that it is almost parallel to PVM).
It can be seen that there are at least two flows (there are at least 3 craters in the area) of Quaternary basalts, Qb, which flowed out onto a sedimentary surface, secondly flowed into river canyons, and finally, which were cut by the latest Virgin River erosion (forming the latest canyon- bypassing some of the older ones). In an outcrop on the north side of the Virgin can be seen the Ps or Pleistocene sediments (rubble), underlying a volcanic tuff- both conformable with each other, but not with the underlying Mesozoic and overlying rock. These are now at a 20 degree unconformity with the underlying sedimentary Triassic rock, Trs. These were laid down by the volcano on the south side of the river, occurring also on the north side by that same volcano (dipping in the opposite direction, as seen below Sky Mountain Golf on the south side of the Virgin), and are tentatively dated as Ps, and show that there was no Virgin River then where they now occur, or to the north of the Radio Tower Volcano. There is also an uplift of the Mesozoic to the east, which indicates a Hogback or tilted monocline pointing northward towards the Pine Valley Mountains; this is not a Laramide structure, although the incipience of the anticline several miles to the north might have been.
From below, the basalt which flowed into the Canyon appears more massive
It appears that the 100k years old vulcanism has created compressive stresses (shoving upward), which accentuated the 100m year Laramide structures in the 200m+ years old Mesozoic rocks. There are several faults and fracture indications in the cliff walls and on the surface Jurassic Navajo Jn on the north side of the River. These generally have a NW-SE trend, which is the normal strain pattern for this part of the Western US over the preceding Epoch (Pliocene) and earlier. The N-S patterns, associated with the recent strains and the Hurricane Fault are not as apparent in this location. One mile to the west and further, river bed directions do have this orientation. In this location the river orients either NW-SE or NE-SW, indicating a transition zone for the stress pattern just west of the Hurricane Fault. This is probably due to the rising vulcanism; some young stream patterns on the east side of the crater orient N-S, indicating the age of the new stress system. The author thinks that this stress change has occurred in the last 2-3 m.y, and that this might be offset by local anomalies, such as vulcanism.
It is believed that the Main Hurricane Fault is one mile east of the volcano, as evidenced by vertical beds at the abandoned Laverkin Power plant on the Virgin River, and the fault extends eastward in splays near the Pah Tempe Hot Springs (a 4000 feet separation). The volcano likely is associated with the uplift of the Colorado Plateau, at the Hurricane fault Hf, but the statistics of volcano location depend upon fracture systems more than upon the plane of the fault- and at the ground surface appear random in areal location.
Several Flows found flat ground, a shallow Virgin canyon, and finally a Gorge