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Roy A. Bailey

Publications and source records attributed to Roy A. Bailey.

15 recordsLinked to original sources
USGS2014

California's restless giant: The Long Valley Caldera

Scientists have monitored geologic unrest in the Long Valley, California, area since 1980. In that year, following a swarm of strong earthquakes, they discovered that the central part of the Long Valley Caldera had begun actively rising. Unrest in the area persists today. The U.S. Geological Survey (USGS) continues to provide the public and civil authorities with current information on the volcanic hazard at Long Valley and is prepared to give timely warnings of any impending eruption.

California↗
USGS2012

Paleomagnetism and K-Ar ages of volcanic rocks from Long Valley caldera, California

Paleomagnetic measurements and K‐Ar age determinations on volcanic rocks from Long Valley caldera, California, have enabled further refinement of eruptive activity within this large silicic volcanic center. K‐Ar age determinations show that postcaldera volcanic eruptions began 0.73 m.y. ago and continued periodically until about 50,000 years ago. The eruptions were not temporally random but tended to occur in distinct episodes separated by periods of quiescence. Volcanism in the western half of the caldera was particularly intense between 0.15 and 0.50 m.y. ago, when many units ranging in composition from basalt to rhyolite were erupted. An average of the virtual geomagnetic poles for 33 units from the caldera yields a paleomagnetic pole at 89.7°N, 138.4°E, (α 95 = 5.1°), which is indistinguishable from the earth's rotational axis. The ancient geomagnetic field dispersion about this mean pole is 16.0°, with upper and lower limits of 19.3° and 13.6°, respectively.

California↗
USGS2004

Eruptive history and chemical evolution of the precaldera and postcaldera basalt-dacite sequences, Long Valley, California: Implications for magma sources, current seismic unrest, and future volcanism

The Long Valley Volcanic Field in east-central California straddles the East Sierran frontal fault zone, overlapping the Sierra Nevada and western Basin and Range Provinces. The volcanic field overlies a mature mid-Tertiary erosional surface that truncates a basement composed mainly of Mesozoic plutons and associated roof pendants of Mesozoic metavolcanic and Paleozoic metasedimentary rocks. Long Valley volcanism began about 4 Ma during Pliocene time and has continued intermittently through the Holocene. The volcanism is separable into two basalt-rhyolite episodes: (1) an earlier, precaldera episode related to Long Valley Caldera that climaxed with eruption of the Bishop Tuff and collapse of the caldera; and (2) a later, postcaldera episode structurally related to the north-south-trending Mono-Inyo Craters fissure system, which extends from the vicinity of Mammoth Mountain northward through the west moat of the caldera to Mono Lake. Eruption of the basalt-dacite sequence of the precaldera basalt-rhyolite episode peaked volumetrically between 3.8 and 2.5 Ma; few basalts were erupted during the following 1.8 m.y. (2.5–0.7 Ma). Volcanism during this interval was dominated by eruption of the voluminous rhyolites of Glass Mountain (2.2–0.8 Ma) and formation of the Bishop Tuff magma chamber. Catastrophic rupture of the roof of this magma chamber caused eruption of the Bishop Tuff and collapse of Long Valley Caldera (760 ka), after which rhyolite eruptions resumed on the subsided caldera floor. The earliest postcaldera rhyolite flows (700–500 ka) contain quenched globular basalt enclaves (mafic magmatic inclusions), indicating that basaltic magma had reentered shallow parts of the magmatic system after a 1.8-m.y. hiatus. Later, at about 400 ka, copious basalts, as well as dacites, began erupting from vents mainly in the west moat of the caldera. These later eruptions initiated the postcaldera basalt-rhyolite episode related to the Mono-Inyo Craters fissure system, which has been active through late Pleistocene and Holocene time.

California↗
USGS2000

Invisible CO2 gas killing trees at Mammoth Mountain, California

Since 1980, scientists have monitored geologic unrest in Long Valley Caldera and at adjacent Mammoth Mountain, California. After a persistent swarm of earthquakes beneath Mammoth Mountain in 1989, geologists discovered that large volumes of carbon dioxide (CO2 ) gas were seeping from beneath this volcano. This gas is killing trees on the mountain and also can be a danger to people. The U.S. Geological Survey (USGS) continues to study the CO2 emissions to help protect the public from this invisible potential hazard.

Fact Sheet↗
USGS1996

Invisible CO2 gas killing trees at Mammoth Mountain, California

Since 1980, scientists have monitored geologic unrest in Long Valley Caldera and at adjacent Mammoth Mountain, California. After a persistent swarm of earthquakes beneath Mammoth Mountain in 1989, earth scientists discovered that large volumes of carbon dioxide (CO 2 ) gas were seeping from beneath this volcano. This gas is killing trees on the mountain and also can be a danger to people. The USGS continues to study the CO 2 emissions to help protect the public from this invisible potential hazard.

California↗
USGS1994

Physical geology and eruptive history of the Matahina Ignimbrite, Taupo Volcanic Zone, North Island, New Zealand

The Matahina Ignimbrite is a 280 ka ash‐flow sheet that erupted from Haroharo Caldera in the Okataina Volcanic Centre, northern Taupo Volcanic Zone, North Island, New Zealand. The ignimbrite underlies a 2000 km 2 area mainly east of the caldera, ranges in thickness from 5 to 200 m, and has a outflow volume of c. 120 km 3 , equivalent to c. 75 km 3 of magma. It is a multiple‐flow, compound cooling unit consisting of a basal tephra (fallout) member and three ash‐flow members, designated lower, middle , and upper , that record three eruptive pulses separated by brief time intervals, estimated from cooling and compaction noddling to range from 20 to 60 days. Distribution of coarse lithic clasts, together with local interbedded co‐ignimbrite lag breccias and tephra layers east of the Puhipuhi Easin, confirm Haroharo Caldera as the eruptive source. Over most of its extent on the Kaingaroa Plateau, the outflow s leet thickens eastward away from its source and attains its greatest thickness in the elongate, north‐trending, fault‐a ngle trough formed between the gently east sloping surface of the plateau and the western front of the Ikawhenua Fange. Difference in thickness of the ignimbrite across the fault bounding the west front of the Ikawhenua Range suggests that during the short time interval between emplacement of the lower and middle ash‐flow members, a major tectonic event caused at least 10 m displacement on the fault locally. Circumstantial evidence supporting this early syneruptive tectonic event is found along the Bay of Plenty coast where penecontemporaneous liquefaction structures, possibly seismically induced, occur in the distal subaqueous facies of the lower ash‐flow member. The presence of such 1 quefaction structures in the Matahina and other coastal New Zealand ignimbrites suggests a possible close association between tectonism and major ignimbrite eruptions.

North Island, Taupo Volcanic Zone↗
USGS1983

The Volcano Hazards Program; objectives and long-range plans

Volcanoes and the products of volcanoes have a much greater impact on people and society than is generally perceived. Although commonly destructive, volcanic eruptions can be spectacularly beautiful and, more importantly, they have produced the very air we breathe, the water we drink, and our most fertile soils. Volcanoes also have a profound effect on climate, and their roots form geothermal energy reservoirs and contain valuable mineral deposits including copper, molybdenum, tin, silver, gold, and diamonds. Of course, volcanoes will continue to erupt whether we understand them or not, but one of the functions of enlightened government and a mission of the U.S. Geological Survey (USGS) is to try to understand and to assess the dangers of volcanic eruptions to our land and people.

Open-File Report↗
USGS1979

Mineral resources of the Minarets Wilderness and adjacent areas, Madera and Mono counties, California

A mineral survey of the Minarets Wilderness area and adjacent areas in the central Sierra Nevada, Calif., was conducted during 1973 through 1975. The total area covers about 620 km 2 (237 sq mi) in the Sierra and Inyo National Forests, of which about 440 km 2 (170 sq mi) are within the officially designated Minarets Wilderness. The mineral resource potential was evaluated by geological, geochemical, and geophysical studies by the U.S. Geological Survey, and by examination of mineralized rocks, prospects, and mining claims by the U.S. Bureau of Mines. The results of the survey indicate that the study area has small to moderate submarginal to paramarginal resources of copper, silver, zinc, lead, iron, and tungsten and an unevaluated potential for molybdenum resources. Limestone is present, but not of commercial quantity or quality. No other industrial minerals have been recognized in quantity. Granitic rocks have potential use as decorative stone and sand and gravel could be produced from either alluvial deposits or glacial drift. However, these commodities are more accessible elsewhere at localities closer to markets. The study area has no potential for fossil fuels, and, because of the general geologic environment, the potential for nuclear fuel minerals is considered to be low. The study area has low geothermal potential, even though it is on the western edge of the Mono-Long Valley "Known Geothermal Resource Area" (KGRA). The area is underlain by metavolcanic and metasedimentary rocks that have been intruded by granitic rocks of the Sierra Nevada batholith. Pliocene volcanic rocks are present locally. With few exceptions, the known occurrences of mineralized rock are confined to the metamorphic rocks, and the exceptions appear to be confined to plutonic rocks that are older than the Late Cretaceous granitic rocks that make up the bulk of the batholithic rocks in the study area. Although no mineral production has been recorded from prospects within the study area, mines adjacent to it have produced significant amounts of gold and tungsten. Production figures are incomplete, but mines in the Mammoth mining district (fig. 1) may have produced as much as $1 million worth of gold, silver, and other metals at the then-existing prices. The Monte Cristo mine in the Mammoth district was in production during 1978.

California↗
USGS1968

Paleomagnetism, potassium-argon ages, and geology of rhyolites and associated rocks of the Valles Caldera, New Mexico

Paleomagnetic and potassium-argon studies support geologic evidence that the lower member of the Bandelier Tuff was deposited 1.4 m.y. ago. The upper member erupted about 1.0 m.y. ago and was followed by caldera collapse which formed the 12- to 14-mile diameter Valles Caldera. Postcaldera activity which resulted in the eruption of rhyolite domes and pyroclastic material, has occurred at about 0.9, 0.7, 0.5, and 0.4 m.y. ago, with later undated eruptions that were estimated at about 0.1 m.y. ago. These data from the Valles Caldera are the basis for the previously published age revision of the Brunhes-Matuyama geomagnetic polarity epoch boundary from 1.0 to 0.7 m.y. ago, and they were used to define the Jaramillo normal polarity event at about 0.9 m.y. ago (Doell and Dalrymple, 1966).

New Mexico↗