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 melng (volcanism) Seafloor spreading results in normal faulng (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. Subducon of the Juan de Fuca/Gorda plate under the North American Plate North American Plate Gorda Plate “Subducon of the oceanic Gorda Plate beneath the North American Plate Mt. Shasta and Lassen Gorda Plate Subducon of the Juan de Fuca/Gorda Plate under North America carries water-logged ocean crust, the water escapes to the overriding mantle and fluxes melng, 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 subducon 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 Locaon 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 connent 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 acve fault zone. Violet zones represent impermeable clay zones or clay filled fractures. If fractures stay open, perhaps through acve faulng, fluid flow can connue Present Day Plate Moons The combinaon of stretching to the east (basin and range), and subducon to the west has led to faulng (potenal permeability), elevated geotherms (volcanism and heat). Geothermal Resources on the Gorda Ridge Basin and range spreading, The snow subducon, and possible hot spot acvity lead to high geotherms and volcanism. Normal faults, associated with volcanism and basin and range spreading (Surprise Valley at least) But are they acve? 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 .