Modoc County & Geothermal Resources & Reserves
Jim McClain, UCD
A Geothermal resource Also known as a hot spring What do you need to have a geothermal resource?
J D F
Blanco FZ
2000 m
Gorda Ridge
GR-14 3000 m (Sea Cliff)
4000 m
The Sea Cliff hydrothermal field, discovered from manned submersible in 1988
Hot Water o ~600 F
Vent chimney Broom handle
Temperature Probe
J D F
Blanco FZ
2000 m
Gorda Ridge
GR-14 3000 m (Sea Cliff)
4000 m
Seafloor Spreading stretches the crust Hot mantle rises to fill in the gap.
Elevated Geotherm in volcanic regions. J D F
Blanco FZ
2000 m
Gorda Ridge Normal faults accommodate the stretching of the crust.
GR-14 3000 m (Sea Cliff)
4000 m
Geothermal Resources on the Gorda Ridge
Seafloor spreading results in rising hot The ocean mantle and mel ng (volcanism)
Seafloor spreading results in normal faul ng (earthquakes), and fracturing of the crust allowing water to pass through. Modoc county hydrothermal system is much more complicated. Volcanic Modoc, plenty of heat, at least at some mes. Subduc on of the Juan de Fuca/Gorda plate under the North American Plate North American Plate Gorda Plate
“Subduc on of the oceanic Gorda Plate beneath the North American Plate Mt. Shasta and Lassen Gorda Plate
Subduc on of the Juan de Fuca/Gorda Plate under North America carries water-logged ocean crust, the water escapes to the overriding mantle and fluxes mel ng, and the Cascade volcanoes result.
The Medicine Lake Volcano, one of a series of volcanoes east of the main Cascades chain. Modoc county has more than just subduc on feeding its volcanoes. Hot spots or “mantle plumes”, from the deep mantle, bring hot mantle close to the surface. Plume tails leave a trail of volcanic islands as the plates move over them.
. A somewhat controversial theory is that the a mantle plume head reached the surface in the northwest about 17 million years ago, and now the tail is reaching the surface under Yellowstone because North America has moved west Current Hot Spot Loca on
If the the theory is correct, then the hot spot “plume head” could have provided some of the volcanism on the Modoc Plateau, but may no long be providing heat today. And last but not least, we have spreading known as the Basin and Range (like the Gorda Ridge, but under a con nent rather than a ocean). The Basin and Range are underlain by very shallow high temperatures. Basin and Range Province, covers much of western Utah, Nevada, and easternmost California, including Surprise Valley. Down drop side
The stretching of the Basin and Range also results in faulting, that could provide fractures for hot fluids. Scarp from the (primarily) faulting that took place during the 1954 Fairview Peak Earthquake in Nevada, from http://www.earth.ox.ac.uk/~andrews/pics.html Modoc County, like much of California, has its faults, but do they provide the permeability needed for a resource, or a reserve. The Model
Impermeable Cap
Cartoon of an anastamosing fracture system, perhaps in an ac ve fault zone. Violet zones represent impermeable clay zones or clay filled fractures. If fractures stay open, perhaps through ac ve faul ng, fluid flow can con nue
Present Day Plate Mo ons
The combina on of stretching to the east (basin and range), and subduc on to the west has led to faul ng (poten al permeability), elevated geotherms (volcanism and heat). Geothermal Resources on the Gorda Ridge
Basin and range spreading, The snow subduc on, and possible hot spot ac vity lead to high geotherms and volcanism.
Normal faults, associated with volcanism and basin and range spreading (Surprise Valley at least) But are they ac ve? A Geothermal resource Also known as a hot spring
Surprise Valley Fault ISO-1 Geothermal Well
H ig h w ay 1 39
• Space He9a Ets 67,000 ft 2 29 •When does a resource become a reserve? When it becomes economical Proviadyes All Domestic Hot Water Geothermal hw • HDigisplacto develop into the needs you have. Example, Canby? es ! 40,000 gal propane/year Discharge • Savings ! $74,000 in 2009 Canby Geothermal, GeoCollab 2010 From Canby 2010, 16 gpm anGeocolabnually