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At least 433 records · Page 24Linked to original sources
USGS1979

Abnormal P-wave delays in The Geysers-Clear Lake Geothermal area, California

Large teleseismic delays, exceeding 1 second, are found near Mount Hannah in the Clear Lake volcanic field and in the steam-production area at The Geysers. The delays are superimposed on a general delay field of about 0.5 second extending over the volcanic rocks and the steam reservoir. It is postulated that a magma chamber under the surface volcanic rocks with a core of severely molten rock beneath Mount Hannah and a highly fractured steam reservoir probably underlain by partially molten rock at The Geysers are responsible for the observed delays. Both zones extend to depths of 20 kilometers or more.

California↗
USGS1986

Changing climate: Geothermal evidence from permafrost in the Alaskan Arctic

Temperature profiles measured in permafrost in northernmost Alaska usually have anomalous curvature in the upper 100 meters or so. When analyzed by heat-conduction theory, the profiles indicate a variable but widespread secular warming of the permafrost surface, generally in the range of 2 to 4 Celsius degrees during the last few decades to a century. Although details of the climatic change cannot be resolved with existing data, there is little doubt of its general magnitude and timing; alternative explanations are limited by the fact that heat transfer in cold permafrost is exclusively by conduction. Since models of greenhouse warming predict climatic change will be greatest in the Arctic and might already be in progress, it is prudent to attempt to understand the rapidly changing thermal regime in this region.

Alaska↗
USGS2001

Taphonomy of silicified filamentous microbes in modern geothermal sinters-Implications for identification

Silicified microbes found on the discharge aprons around modern geysers and hot springs commonly appear to be preserved superbly. This can be attributed to their rapid silicification, which often begins while they are alive. In geological terms, therefore, they are silicified instantaneously. Thus, it might be expected that these microbes should be good replicas of the living organisms and, therefore, easy to identify in terms of extant taxa. Silicified microbes found on the discharge aprons around geysers and hot springs of North Island, New Zealand, are preserved through replacement and/or encrustation. Organic matter is typically absent, and examples of sheaths being partly replaced or coated by other minerals, such as iron oxide, have not yet been recognized. Accordingly, the cellular-level information needed for microbe identification must be gleaned from features preserved in the silica. Unfortunately, the silicification processes commonly destroy and/or disguise most of the taxonomic features that are necessary for reliable identification in terms of extant taxa. Silicification may, for example, obscure the presence of a sheath and/or significantly alter the size of the microbes. The loss and/or modification of such important taxonomic features means that the identification of silicified microbes is fraught with problems and must be approached with caution.

Palaios↗
USGS1920

Geothermal data of the United States, including many original determinations of underground temperature

The purpose of this report is to present all available published data bearing on the rate of increase of underground temperature with increasing depth in the United States, together with several hundred original observations by myself and my associates. A canvass of the governmental, State, and serial publications has yielded many records of temperature of flowing wells and also a few observations made with thermometers in borings and deep mines. Additional data on temperature of flows have been given by correspondents. Some of the data, especially those relating to flows from wells, may not be reliable, and as a rule these could not be discriminated. Many records are omitted because no facts are available as to the source of flow.

Bulletin↗
USGS2019

Digital database of the geologic map of the middle east rift geothermal subzone, Kīlauea Volcano, Hawai‘i

This database release contains all the information used to produce Geologic Investigations Series I-2614 ( https://pubs.usgs.gov/imap/2614/ ). The main component of this digital release is a geodatabase prepared using ArcGIS, but Esri shapefiles are included as well. Kīlauea is an active shield volcano in the southeastern part of the Island of Hawai‘i. The middle East Rift Zone (MERZ) map includes about 27 square kilometers of the MERZ and shows the distribution of the products of 34 separate eruptions during late Holocene time. Lava flows erupted during 1983–86 have reached the mapped area. The subaerial part of the MERZ is 3–4 km wide and about 18 km long. It is a constructional ridge, 50–150 m above the adjoining terrain, marked by low spatter ramparts and cones as high as 60 m. Lava typically flowed either northeast or southeast, depending on vent location relative to the topographic crest of the rift zone. The MERZ receives more than 100 inches of rainfall annually and is covered by tropical rain forest. Vegetation begins to grow on lava a few months after its eruption. Relative heights of trees can be a guide to relative ages of underlying lava flows, but proximity to faults, presence of easily weathered cinders, and human activity also affect the rate of growth. The rocks have been grouped into five basic age groups. The framework for the ages assigned is provided by eight radiocarbon ages from nearby mapping by the authors and a single date from within this investigation area. The numerical ages are supplemented by observations of stratigraphic relations, degree of weathering, soil development, and vegetative cover.

Hawaii↗