Geology Across and Under the Western Snake River Plain, Idaho: Owyhee Mountains to the Boise Foothills

This 1-day field trip is a transect across the western Snake River Plain (fig. 1). The western plain is a continental- rift structure, 300 km long and 70 km wide. It is bounded and internally faulted by northwest-trending normal faults. The western Snake River Plain has a different orientation and structure than the eastern plain. The eastern plain is a curious downwarp related to magmatism and extension along the track of the Yellowstone hot spot (fig. 2). The faulted basin of the western plain began forming about 12 m.y. ago, and much of the relief was completed by 9 Ma. This timing corresponds with the passage of the hot spot located to the south about 11 Ma. Wood and Clemens (2002) suggest that softening of the lithosphere by the passing hot spot triggered extension and basin formation. The hot spot passage was accompanied by voluminous rhyolite volcanism to the south and by eruptions of rhyolite at or near the margins of the western plain (Bonnichsen and others, 2004; Perkins and Nash, 2002; Pierce and Morgan, 1992). Northwest of the western plain and in southeastern Oregon voluminous eruptions of the Columbia River and Steens Mountains flood basalts occurred between 16.1 and 15.0 Ma (Hooper and others, 2002a, 2002b; Camp and others, 2003). Earliest Columbia River basalts are as old as 17.5 Ma (Baksi, 2004

Vertical Variation in Groundwater Chemistry Inferred from Fluid Specific-Conductance Well Logging of the Snake River Plain Basalt Aquifer, Idaho National Engineering Laboratory, Southeastern Idaho

Well logging of electrical fluid specific conductance (Cs) shows that permeable zones yielding ground water to intrawell flows and the water columns in some wells at INEL have highly different chemistry, with as much as a two-fold variation in Cs). This suggests that dedicated pump sampling of ground water in the aquifer may not be representative of the chemistry of the waste plumes migrating southwest of the nuclear facilities. Natural background Cs in basalt-aquifer ground water of this part of the Snake River Plain aquifer is less than 325µS/cm (microSiemans/cm), and total dissolved solids in mg/L units, (TDS) ≈ 0.6Cs). This relationship underestimates IDS for waters with chemical waste. when Cs) is above 800 µS/cm. At well 59 near the ICPP water of 1115 µS/cm (≈670+ mg/L TDS) enters the well from a permeable zone between 521 and 537 ft depth; the zone being 60 ft below the water level and water of 550 µS/cm. At the time of logging (9/14/93) the 1115µS/cm water was flowing down the well, mixing with less concentrated waters and exiting at 600 or 624-ft depth. Waste water disposed of down the injection well at ICPP until 1984 was estimated to have a Cs) of 1140 µS/cm, identical to the water detected in logging. At well OW2, the highest Cs) water (760µS/cm) is in the upper 30 feet of the water column: water from two flow zones below have different chemistry with lower values of Cs. The Site 14 well and USGS 83 show uniform values throughout the water column. The water column in Site 14 is dominated by a downward flow of 50 gal/min probably entering between 475 and 500 ft depth and exiting near the bottom of the well at 700 ft depth. Impeller flowmeter and precision temperature logging are used to define and quantify temperature variations and intrawell flows. At well 59 (depth=657 ft) and OW2 (depth=996 ft), are downward decreasing temperatures in the bottom zones of no flow, suggesting that major flow zones lie beneath the deepest parts of these wells

Terminal Moraine Remnants of the Trail Creek Glacier Northeast of Sun Valley, Idaho

This optional excursion is 8 miles on paved road from the center of Ketchum (Main Street and Sun Valley Road traffic light), northeast through Sun Valley along the Trail Creek Road (fig. 1). A short walk of 10 minutes takes you to the crests of two moraines of very different ages. Here we view and discuss calcareous soils developed into the deposits, the pretty weathering-rinds developed on the sandstone cobbles, and ages of Pinedale and Bull Lake advances. During the Quaternary, an extensive system of mountain glaciers accumulated in the Pioneer and Boulder Mountains and flowed down valleys emanating from the ranges (Evenson and others, 1982, Pearce and others, 1988). An ice field several miles across accumulated in the Trail Creek Summit area and contributed ice to both the northeast-flowing Summit Creek glacier and to south-flowing Trail Creek glacier (fig. 2). Despite barroom talk in Sun Valley and Ketchum, we find no evidence that the resort towns or the Mt. Baldy ski hill were glaciated during the last ice ages. Rather, the glacier of closest approach was the Trail Creek glacier that advanced down valley to about elevation 1,950 m (6,400 ft), where Wilson Creek flows into Trail Creek, about 10 km (6 mi) northeast of the Sun Valley Inn. The remnants of the two terminal moraines are best seen on the spur at the confluence of Wilson Creek and Trail Creek (fig. 3). From the road, facing northeast, the moraines appear as low ridges sloping 12º from the walls of Trail Creek Canyon down to Wilson Creek Canyon. Crest of the upper moraine stands 55 m higher than the lower moraine. The 12º crestal slope down into Wilson Creek, and low position in the valley indicate that this was the terminus of the two glacial advances. Furthermore, only outwash sand and gravel terraces occur below this area; no till or erratics are observed on the canyon walls down valley

Geothermal Systems of Northern Thailand and Their Association with Faults Active During the Quaternary

Many of northern Thailand hot springs systems are associated with regions of active faulting. An arcuate pattern of wells with high-fluoride water occurs in the Chiang Mai basin. The pattern is parallel to the Mae Tha fault which cuts Paleozoic and Mesozoic rocks 10 km east of the basin. The San Kamphaeng geothermal system is within parallel faults in Paleozoic rocks. The Mae Tha fault is believed to be active in the Quaternary. A conceptual diagram shows deep groundwater circulation driven by ~300 to 800 meters of relief in the hills east of the basin. The Mae Chan geothermal system lies along the active, left-lateral, strike-slip Mae Chan fault in northernmost Thailand. The Mae Chan hot springs emanate from Triassic granitic rocks in the fault zone. Several other hot springs emanate from the along the fault. It appears that late Cenozoic activity along faults creates permeability that allows upward flow of deep (\u3e 2 km) percolating groundwater. These systems are currently being evaluated by geothermometry of water chemistry, geophysical exploration, and detailed geologic mapping. Aim is to establish drilling locations for wells that will provide 2-5 MWe of power generation

Turbidity-Based Sediment Monitoring in Northern Thailand: Hysteresis, Variability, and Uncertainty

Annual total suspended solid (TSS) loads in the Mae Sa River in northern Thailand, determined with an automated, turbidity-based monitoring approach, were approximately 62,000, 33,000, and 14,000 Mg during the three years of observation. These loads were equivalent to basin yields of 839 (603-1170), 445 (217-462), and 192 (108-222) Mg km-2 for the 74.16-km2 catchment during 2006, 2007, and 2008, respectively. The yearly uncertainty ranges indicate our loads may be underestimated by 38-43% or overestimated by 28-33%. In determining the annual loads, discharge (Q) and turbidity (T) values were compared against 333 hand-sampled total suspended solid concentrations (TSS) measured during 18 runoff events and other flow conditions across the three-year period. Annual rainfall varied from 1632 to 1934 mm; and catchment runoff coefficients (annual runoff/annual rainfall) ranged from 0.25 to 0.41. Measured TSS ranged from 8-15,900 mg l-1; the low value was associated with dry-season base flow; the latter, a wet-season storm. Storm size and location played an important role in producing clockwise, anticlockwise, and complex hysteresis effects in the Q-TSS relationship. Turbidity alone was a good estimator for turbidity ranges of roughly 10-2800 NTU (or concentrations approximately 25-4000 mg l-1). However, owing to hysteresis and high sediment concentrations that surpass the detection limits of the turbidity sensor during many annual storms, TSS was estimated best using a complex multiple regression equation based on high/low ranges of turbidity and Q as independent variables. Turbidity was not a good predictor of TSS fractions \u3e 2000 μm. Hysteresis in the monthly Q-TSS relationship was generally clockwise over the course of the monsoon season, but infrequent large dry-season storms disrupted the pattern in some years. The large decrease in annual loads during the study was believed to be related to depletion of fine sediment delivered to the stream by several landslides occurring the year prior to the study. The study indicated the importance of monitoring Q and turbidity at fine resolutions (e.g., sub-hourly) to capture the TSS dynamics and to make accurate load estimations in this flashy headwater stream where hysteresis in the Q-TSS signature varied at several time scales

Natural Degradation of Earthworks, Trenches, Walls and Moats, Northern Thailand

“………..structures of this kind are hidden away securely under the thick overgrowth: thus does nature preserve what man would surely destroy” (from Sumet Jumsai, 1970) We investigate the geometry, age, and history of several enigmatic northern Thailand earthwork entrenchments that are mostly located on hills and could not have held water to form moats. The earthworks are either oval or rectangular in map view; and they typically encircle 0.3-to-1-km2 areas that do not have potsherd debris indicative of former towns. Most trenches are 3-5 m deep with inner walls 4.5-8 m high. Some encircling earthworks are concentric double trenches spaced approximately 10 m apart. Historians have suggested these earthworks enclosed defensible areas where people in outlying villages sought refuge when under attack by neighboring rulers, the Chinese Ho, or the Burmese. We believe that some encircling entrenchments may have been for the capture or containment of elephants. Nearly all of the once near-vertical original walls have degraded to slopes of 32-47°. Fitting calculated curves of the diffusion-based scarp-degradation model to our height-slope data, and assuming most scarps have degraded since the end of La Na Kingdom time A.D. 1558. We derive a diffusion coefficient of 0.002 m2 y-1. Slopes of the rectangular earthwork at Souvannkhomkham, Laos, across the Mekong River from Chiang Saen Noi, are significantly more degraded (approximately 32°), indicating an age of 800-1200 years. Locations of these earthworks are established in hope that they will be preserved as part of the Thai and Lao archaeological legacy

Recent Paleoseismic Investigations in Northern and Western Thailand

Recent paleoseismic investigations have identified a number of active faults in Northern and Western Thailand. Northern Thailand is an intraplate basin and range province, comprised of north-south-trending Cenozoic intermontane grabens and half grabens, bounded by north- to northwest-striking normal to normal-oblique faults and northeast-striking left-lateral strike-slip faults. The basin-bounding normal faults are marked by steep, linear range fronts with triangular facets and wineglass canyons and have slip rates of 0.1 to 0.8 mm/yr. Based on limited data, the average vertical displacement-per-event is about 1.0 to 1.5 m. These faults are characterized by recurrence intervals of thousands to tens of thousands of years and are capable of generating earthquakes up to moment magnitude (M) 7, and larger. The northeast-striking strike-slip faults are marked by shutter ridges, and deflected drainages. Slip rates are 3 mm/yr or less. Western Thailand is dissected by a number of northwest- and north-northwest-striking, right-lateral strike-slip faults related to the Sagaing Fault in Myanmar. Although showing much less activity than the faults in neighboring Myanmar, these faults display abundant evidence for late Quaternary movement, including shutter ridges, sag ponds, and laterally offset streams. The slip rate on these faults is estimated to be 0.5 to 2.0 mm/yr. These faults are considered capable of generating maximum earthquakes of up to M 71/2

Floodplain Deposits, Channel Changes and Riverbank Stratigraphy of the Mekong River Area at the 14th-Century City of Chiang Saen, Northern Thailand.

Riverbank stratigraphy and paleochannel patterns of the Mekong River at Chiang Saen provide a geoarchaeological framework to explore for evidence of Neolithic, Bronze-age, AD 5th Century Yonok and AD 14-16th Century Lan Na Cultures. Typical bank stratigraphy charted on the Thailand side is imbricate cobble gravel overlain by 5-10 m of reddish-brown sandy silt. The silt section is composed chiefly of ½ to 2-m thick layers of massive silt without paleosols interpreted as near-channel floodplain and gently-inclined levee deposits laid down by episodic, infrequent, large floods. The surface soil is dark-brown clay loam (La Na time. Brick ruins of 14-16th Century Buddhist temples are crumbling into the river at Chiang Saen Noi, and formerly did so at Chiang Saen until banks were stabilized by rock walls. Bank retreat from river erosion has been \u3e20 m since La Na time, and has exposed a siltfilled moat. A radiocarbon age of 1475 cal yr AD was obtained from charcoal at the bottom of the moat, beneath 5.6 m of silt. Lag material from erosion of the silt banks contains Neolithic and Bronze Age artifacts out of stratigraphic context, as well as ceramics and bricks of La Na age. These artifacts as well Neolithic artifacts obtained from a 1972 excavation near the mouth of the Kham River indicate long human habitation of this riverbank area. In northern Thailand the Mekong is mostly in a bedrock canyon, but shifting topography along the active strike-slip Mae Chan fault has formed the upstream 2-5-km wide floodplain at Chiang Saen, and downstream has diverted the river into a broad S-shaped loop in the otherwise straight course of the river. A 1.7-Ma basalt within the bedrock channel 45-km downstream of Chiang Saen indicates little vertical incision by the river. Satellite images show former channels in the Chiang Saen area, meander-point-bar scrolls (radii of curvature \u3e 1.2 km), and floodplain edges as arcuate cuts of similar curvature into the saprolite-mantled bedrock hills These features indicate channel avulsion occurred by meander loop cutoff in the past. Brick Buddhist monuments of the 14th-16th Century were built upon the floodplain with meander features on the Thai and Laos side of the river, indicating that these meandering channel features and the broader floodplain are mostly older than 600 years

Chronology of Late Pleistocene and Holocene Volcanics, Long Valley and Mono Basin Geothermal Areas, Eastern California

Hydration-rind ages based on hydration-rind thicknesses of obsidian and an assumed hydration rate of 5 microns2/1000 yrs have been determined for the 26 exposed Mono domes and coulees. Hydration-rind thickness data give good estimates of relative age differences between the domes, but determination of absolute ages will depend upon calibration to radiometric ages. The first extrusion of highly differentiated, sparsely porphyritic rhyolite occurred an estimated 32,000 to 40,000 yrs ago and consists of a small dome at the northwest end of the contiguous chain. The next major extrusive event occurred about 24,000 yrs ago and is represented by two domes and a major tephra. About 10,000 yrs ago, the frequency of eruptive activity increased, and rhyolite lava was extruded at an average rate of 0.2 km3/1000 yrs; periods of dormancy ranging in length from 300 to 2000 yrs. About 2000 to 3000 yrs ago the rate of extrusion increased dramatically to 0.8 km3/1000 yrs beginning with the eruption of the South Coulee and its associated tephra. At the same time, the nature of erupted magma changed from sparsely porphyritic (3 to 10 per cent sanidine) to aphyric rhyolite. All eruptions since 2000 radiocarbon yrs BP have produced magma that is aphyric but is of the same chemical composition as the earlier porphyritic magma. Volumes of porphyritic and aphyric extrusives, each of which includes volumes of lava and volumes of pumiceous pyroclastics reduced for porosity, are nearly equal and together total about 4 km3. Projecting the recent rate of extrusion over the time since the last major eruption, 1185 radiocarbon yrs ago suggests that a future eruption in the Mono Chain could release as much as 1 km3 of magma. The recent increase in extrusion rate and the contemporaneous change in the nature of the magma are attributed to an event in the magma chamber that allowed the release of hotter, more fluid, crystal-free magma. The young age for the beginning of rhyolite volcanism from the Mono magma chamber suggests that rhyolite magma may have been emplaced in the shallow crust as recently as 32,000 to 40,000 yrs ago. Calculations by Lachenbruch et al. (1976, Jour. Geophys. Research, v. 81, p. 769-784) that a thermal disturbance at this age would have propagated upward by solid conduction only 4 km and offer an explanation for the lack of a heat-flow anomaly and surface indications of hydrothermal activity over the Mono magma chamber and its associated ring-fracture system. This report also contains new information on the age and chemistry of volcanics on the Mono Lake islands, the Inyo domes, and tephras within the Long Valley Caldera. A newly discovered rhyolite tuff ring of late Quaternary age in the Toowa volcanic field of the southern Sierra Nevada is briefly described for it represents a new area that should be examined for potential as a geothermal area

Geologic Framework of the Fang Hot Springs Area with Emphasis on Structure, Hydrology, and Geothermal Development, Chiang Mai Provence, Northern Thailand

Geologic mapping, a magnetotelluric survey, well data, and earlier reports are integrated to guide further development of the Fang geothermal system. The Fang Hot Springs originally flowed ~ 20 l s−1 of 90–99 °C water from a 10-hectare area of crystal- line rocks presumed to be of Triassic age. Four wells 92–500 m deep now flow ~ 20 l s−1 of 110–115 °C water and generate 115–250 kWe from the 1989 Ormat binary power plant. Wells are not pumped nor is the spent water re-injected. Temperatures of 130 °C occur in some wells and water chemistry indicates reservoir temperatures of 150 °C. The springs now flow ~ 10 l s−1 . The Fang geothermal area is at the west end of the active left-lateral strike-slip Mae Chan fault (MCF). MCF transitions to extensional faulting along the western boundary of the Cenozoic Fang basin. The hot waters emanate from crystalline rocks 0.7 km north of the MCF. Permeable fractures may be tensile fractures at the right-stepping fault tip. The less permeable MCF fault core and Cenozoic sediments of the Fang basin to the SW are not considered to be drilling targets. Unrelated to the fracture system is the Doi Kia detachment fault which places Paleozoic sediments over crystalline rock with a low-angle contact. Electrical resistivity surveys detect low resistivity (\u3c 60 Ωm) only within the upper 50–100 m of the hot springs area. Deeper crystalline rock is \u3e 100 Ωm. Low resistivity is caused mostly by conductive minerals of hydrothermal alteration, and not by the geothermal water of resistivity 5.6 Ωm. No deep resistivity anomaly is detected beneath the seeps or producing wells, although resolution of past surveys would not have imaged narrow zones of alteration. High-resolution resistivity surveys focused on detecting the deeper fracture system are recommended over the hot well area and south over the area underlain by crystalline rocks. Future development should focus on drilling wells (≤ 500 m) with diameters large enough to install submersible pumps to increase flows. Development of several MWe may be possible and should include a designed re-injection well system to sustain pump levels