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J.R. Riehle

Publications and source records attributed to J.R. Riehle.

At least 19 recordsLinked to original sources
USGS2017

Heterogeneity, Correlatives, and Proposed Stratigraphic Nomenclature of Hayes Tephra Set H, Alaska

Several Holocene tephra deposits of Hayes volcano constitute a marker horizon in southern and east-central Alaska. Their identification is aided by high amphibole/pyroxene ratio and biotite in trace amounts, unique among Holocene tephra deposits of the region. However, correlations are obscured by chemical heterogeneity of the glass which occurs at a scale less than the size of a lapilli. Single-shard analyses confirm that the heterogeneity is due neither to fractionation nor to plagioclase microlites. The heterogeneity may be due to mixing of magmas prior to eruption. It is proposed that the deposits be informally called Hayes tephra set H.

Quaternary Research↗
USGS2017

The Hayes tephra deposits, and upper Holocene marker horizon in south-central Alaska

The most widespread of all Holocene tephra deposits in the Cook Inlet region of south-central Alaska is a set of deposits from Hayes volcano. Because of their unique phenocryst content-biotite in rare amounts and a high proportion of amphibole to pyroxene-the deposits are readily identifiable at all but the most distant sites where they are very fine grained. Eighteen radiocarbon dates from eight upland sites limit the age of the tephra set to between about 3500 and 3800 yr. The set originated at Hayes volcano in the Tordrillo Mountains 150 km northwest of Anchorage; seven or possibly eight closely succeeding deposits, low-silica dacite in composition, compose two main lobes that extend northeast for 400 km and south for at least 250 km from the vent. We estimate the total tephra volume to be 10 km3; multiple layers imply four to six larger and two or three smaller eruptions. The deposits are a nearly isochronous marker horizon that should be useful in future archeologic, geologic, and palynologic studies in the region. ?? 1990.

Quaternary Research↗
USGS2017

The Mount Edgecumbe tephra deposits, a marker horizon in southeastern Alaska near the Pleistocene-Holocene boundary

Late Pleistocene tephra deposits found from Sitka to Juneau and Lituya Bay are assigned to a source at the Mount Edgecumbe volcanic field, based on similarity of glass compositions to nearvent deposits and on thinning away from Kruzof Island. The sequence of near-vent layers is basaltic andesite and andesite at the base, rhyolite, and mixed dacite and rhyolite on top. The only breaks in the tephra sequence are two 1-mm-thick silt partings in a lake-sediment core, indicating a depositional interval from basaltic andesite to dacite of no more than about a millennium. Tephra deposits at sites >30 km from the vent are solely dacite and rhyolite and are 10,600 to 11,400 14C yr old based on interpretation of 18 radiocarbon ages, including 5 by accelerator mass spectrometry (AMS). Basaltic andesite and andesite deposits nearer the vent are as much as 12,000 yr old. Discrepancy among radiocarbon ages of upland tephra deposits provisionally correlated as the same grainfall is resolvable within ??2 ?? of analytical uncertainty. Comparison of bulk and AMS ages in one sediment core indicates a systematic bias of +600 to +1100 yr for the bulk ages; correlation of tephra deposits among upland and lacustrine sites implies an additional discrepancy of 200-400 yr between upland (relatively too young) and lacustrine ages. In any case, the Mount Edgecumbe tephra deposits are a widespread, latest Pleistocene stratigraphic marker that serves to emphasize the uncertainty in dating biogenic material from southeastern Alaska. ?? 1992.

Quaternary Research↗
USGS2008

Stratigraphic and compositional complexities of the late Quaternary Lethe tephra in South-central Alaska

Recently discovered Lethe tephra has been proposed as a latest Pleistocene marker bed in Bristol Bay lowland NE to the Cook Inlet region, Alaska, on the basis of correlations involving a single "Lethe average" glass composition. Type deposits in the Valley of Ten Thousand Smokes, however, are chemically heterogeneous-individual lapilli as well as aggregate ash deposits have glass compositions that range from the average mode to much higher SiO2 and K2O. Moreover, a lake-sediment core from the Cook Inlet region contains one ash deposit similar to "Lethe average" and other, closely underlying deposits that resemble a mixture of the average mode and high-Si high-K mode of proximal deposits. Synthesis of previously published radiocarbon ages indicates a major eruption mainly of "Lethe average" mode about 13,000 14C yr BP. As many as six deposits in the Cook Inlet region-five chiefly "Lethe average" mode-range from about 13,000 to 15-16,000 14C yr BP, and an early Holocene deposit in the Bristol Bay lowland extends the minimum age range of Lethe tephra throughout this region to 8000 14C yr BP. Because of the appearance of "Lethe average" composition in multiple deposits spanning thousands of years, we urge caution when using a Lethe-like composition as a basis for inferring a latest Pleistocene age of a tephra deposit in south-central Alaska. Linear variation plots suggest that magma mixing caused the Lethe heterogeneity; multiple magmas were involved as well in other large pyroclastic eruptions such as Katmai (Alaska) and Rotorua (New Zealand). Lethe is an example of a heterogeneous tephra that may be better compared with other tephras by use of plots of individual analytical points rather than by calculating similarity coefficients based on edited data. ?? 2006 Elsevier Ltd and INQUA.

Quaternary International↗
USGS2000

Tephrochronology of the Brooks River Archaeological District, Katmai National Park and Preserve, Alaska: What can and cannot be done with tephra deposits

The Brooks River Archaeological District (BRAD) in Katmai National Park and Preserve is a classical site for the study of early humans in Alaska. Because of proximity to the active Aleutian volcanic arc, there are numerous tephra deposits in the BRAD, which are potentially useful for correlating among sites of archaeological investigations. Microprobe analyses of glass separates show, however, that most of these tephra deposits are heterogeneous mixtures of multiple glass populations. Some glasses are highly similar to pyroclasts of Aniakchak Crater (160 km to the south), others are similar to pyroclasts in the nearby Valley of Ten Thousand Smokes, and some are similar to no other tephra samples from the Alaska Peninsula. Moreover, tephra deposits in any one archaeological study site are not always similar to those from nearby sites, indicating inconsistent preservation of these mainly thin, fine-grained deposits. At least 15, late Holocene tephra deposits are inferred at the BRAD. Their heterogeneity is the result of either eruptions of mixed or heterogeneous magmas, like the 1912 Katmai eruption, or secondary mixing of closely succeeding tephra deposits. Because most cannot be reliably distinguished from one another on the basis of megascopic properties, their utility for correlations is limited. At least one deposit can be reliably identified because of its thickness (10 cm) and colour stratification. Early humans seem not to have been significantly affected by these tephra falls, which is not surprising in view of the resilience exhibited by both plants and animals following the 1912 Katmai eruption.

Alaska↗
USGS1999

Data on Holocene tephra (volcanic ash) deposits in the Alaska Peninsula and lower Cook Inlet region of the Aleutian volcanic arc, Alaska

This site provides information about the number, thickness, and grainsize of Holocene volcanic ash deposits at 50 localities in the eastern Aleutian volcanic arc. In addition, the major-element compositions of the glasses separated from more than 350 samples of tephra from these localities, determined by electron microprobe, are presented as a basis for correlating samples. Where known with reasonable certainty, the source of an analyzed sample is also identified for use in comparative studies of magma chemistry.

Alaska↗
USGS1998

Catalog of the historically active volcanoes of Alaska

Alaska hosts within its borders over 80 major volcanic centers that have erupted during Holocene time (< 10,000 years). At least 29 of these volcanic centers (table 1) had historical eruptions and 12 additional volcanic centers may have had historical eruptions. Historical in Alaska generally means the period since 1760 when explorers, travelers, and inhabitants kept written records. These 41 volcanic centers have been the source for >265 eruptions reported from Alaska volcanoes. With the exception of Wrangell volcano, all the centers are in, or near, the Aleutian volcanic arc, which extends 2500 km from Hayes volcano 145 km west of Anchorage in the Alaska-Aleutian Range to Buldir Island in the western Aleutian Islands (fig. 1). The volcanic arc, a subduction-related feature associated with underthrusting of the Pacific plate beneath the North American plate is divided between oceanic island arc and continental margin segments, the boundary occurring at about 165° W longitude (fig. 1). An additional 7 volcanic centers in the Aleutian arc (table 2; fig. 1 A) have active fumarole fields but no reported historical eruptions. This report discusses the location, physiography and structure, eruptive history, and geology of those volcanoes in Alaska that have experienced one or more eruptions that have been recorded in the written history (i.e., in historical time). It is part of the group of catalogs entitled Catalogue of Active Volcanoes of the World published beginning in 1951 under the auspices of the International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI). A knowledge of the information contained in such catalogs aids in understanding the type and scale of activity that might be expected during a particular eruption, the hazards the eruption may pose, and even the prediction of eruptions. The catalog will thus be of value not only to the inhabitants of Alaska but to government agencies concerned with emergency response, air traffic operations, and weather, as well as to industry and scientists. The combination of the hazard posed by volcanic ash to jet aircraft and the heavy use of international air routes located parallel to, and on either side of, the Aleutian volcanic arc means that even remote volcanoes in Alaska now pose significant hazards to life and property. Although this report is concerned with historical eruptions from Alaskan volcanoes, other volcanoes in Alaska have erupted in the past 10,000 years and might therefore be expected to erupt again. Several Holocene volcanic centers in the Aleutian arc have no reported historical activity. Elsewhere in Alaska the Bering Sea basalt fields cover large areas of the Yukon Delta, Seward Peninsula, and several of the islands of the Bering Sea. Holocene centers also occur in the Wrangell Mountains and in isolated occurrences in the interior and southeastern Alaska. Eruptions from these centers have occurred within the past several hundred years but none were transcribed in the written record. Moodie and others (1992), however, report oral traditions among the Northern Athapaskan Indians of the southwestern Yukon Territory that may record the second and younger deposition of the White River Ash circa A.D. 720. This lobe of the White River Ash was deposited during the paroxysmal eruption of Churchill volcano in the Wrangell Mountains of eastcentral Alaska (McGimsey and others, 1992; Richter and others, 1995).

Alaska↗
USGS1997

Digital shaded-relief image of Alaska

One of the most spectacular physiographic images of the conterminous United States, and the first to have been produced digitally, is that by Thelin and Pike ( USGS I-2206, 1991 ). The image is remarkable for its crispness of detail and for the natural appearance of the artificial land surface. Our goal has been to produce a shaded-relief image of Alaska that has the same look and feel as the Thelin and Pike image. The Alaskan image could have been produced at the same scale as its lower 48 counterpart (1:3,500,000). But by insetting the Aleutian Islands into the Gulf of Alaska, we were able to print the Alaska map at a larger scale (1:2,500,000) and about the same physical size as the Thelin and Pike image. Benefits of the 1:2,500,000 scale are (1) greater resolution of topographic features and (2) ease of reference to the U.S. Geological Survey (USGS) (1987) Alaska Map E and the statewide geologic map (Beikman, 1980), which are both 1:2,500,000 scale. Manually drawn, shaded-relief images of Alaska's land surface have long been available (for example, Department of the Interior, 1909; Raisz, 1948). The topography depicted on these early maps is mainly schematic. Maps showing topographic contours were first available for the entire State in 1953 (USGS, 1:250,000) (J.H. Wittmann, USGS, written commun., 1996). The Alaska Map E was initially released in 1954 in both planimetric (revised in 1973 and 1987) and shaded-relief versions (revised in 1973, 1987, and 1996); topography depicted on the shaded-relief version is based on the 1:250,000-scale USGS topographic maps. Alaska Map E was later modified to include hypsometric tinting by Raven Maps and Images (1989, revised 1993) as copyrighted versions. Other shaded-relief images were produced for The National Geographic Magazine (LaGorce, 1956; 1:3,000,000) or drawn by Harrison (1970; 1:7,500,000) for The National Atlas of the United States. Recently, the State of Alaska digitally produced a shaded-relief image of Alaska at 1:2,500,000 scale (Alaska Department of Natural Resources, 1994), using the 1,000-m digital elevation data set referred to below. An important difference between our image and these previous ones is the method of reproduction: like the Thelin and Pike (1991) image, our image is a composite of halftone images that yields sharp resolution and preserves contrast. Indeed, the first impression of many viewers is that the Alaskan image and the Thelin and Pike image are composites of satellite-generated photographs rather than an artificial rendering of a digital elevation model. A shaded-relief image represents landforms in a natural fashion; that is, a viewer perceives the image as a rendering of reality. Thus a shaded-relief image is intrinsically appealing, especially in areas of spectacular relief. In addition, even subtle physiographic features that reflect geologic structures or the type of bedrock are visible. To our knowledge, some of these Alaskan features have not been depicted before and so the image should provide earth scientists with a new "look" at fundamental geologic features of Alaska.

Alaska↗
USGS1995

Cooling, degassing and compaction of rhyolitic ash flow tuffs: A computational model

Previous models of degassing, cooling and compaction of rhyolitic ash flow deposits are combined in a single computational model that runs on a personal computer. The model applies to a broader range of initial and boundary conditions than Riehle's earlier model, which did not integrate heat and mass flux with compaction and which for compound units was limited to two deposits. Model temperatures and gas pressures compare well with simple measured examples. The results indicate that degassing of volatiles present at deposition occurs within days to a few weeks. Compaction occurs for weeks to two to three years unless halted by devitrification; near-emplacement temperatures can persist for tens of years in the interiors of thick deposits. Even modest rainfall significantly chills the upper parts of ash deposits, but compaction in simple cooling units ends before chilling by rainwater influences cooling of the interior of the sheet. Rainfall does, however, affect compaction at the boundaries of deposits in compound cooling units, because the influx of heat from the overlying unit is inadequate to overcome heat previously lost to vaporization of water. Three density profiles from the Matahina Ignimbrite, a compound cooling unit, are fairly well reproduced by the model despite complexities arising from numerous cooling breaks. Uncertainties in attempts to correlate in detail among the profiles may be the result of the non-uniform distribution of individual deposits. Regardless, it is inferred that model compaction is approximately valid. Thus the model should be of use in reconstructing the emplacement history of compound ash deposits, for inferring the depositional environments of ancient deposits and for assessing how long deposits of modern ash flows are capable of generating phreatic eruptions or secondary ash flows.

Bulletin of Volcanology↗
USGS1994

Rare earth element contents and multiple mantle sources of the transform-related Mount Edgecumbe basalts, southeastern Alaska

Pleistocene basalt of the Mount Edgecumbe volcanic field (MEF) is subdivided into a plagioclase type and an olivine type. Olivine basalt crops out farther inboard from the nearby Fairweather transform than plagioclase basalt. Th/La ratios of plagioclase basalt are similar to those of mid-ocean-ridge basalt (MORB), whereas those of olivine basalt are of continental affinity. The olivine basalt has higher 87 Sr/ 86 Sr ratios than the plagioclase basalt.We model rare earth element (REE) contents of the olivine basalt, which resemble those of transitional MORB, by 10–15% partial melting of fertile spinel–plagioclase lherzolite followed by removal of 8–13% olivine. Normative mineralogy indicates melting in the spinel stability field. REE contents of an undersaturated basalt (sample 5L005) resemble those of Mauna Loa tholeiite and are modelled by 5–10% partial melting of fertile garnet lherzolite followed by 10% olivine removal. Plagioclase basalt resembles sample 5L005 in REE contents but is lower in other incompatible-element contents and 87 Sr/ 86 Sr ratios. Plagioclase basalt either originated in depleted garnet lherzolite or is a mixture of sample 5L005 and normal MORB; complex zoning of plagioclase and colinear Sc and Th contents are consistent with magma mixing.We conclude that olivine basalt originated in subcontinental spinel lherzolite and that plagioclase basalt may have originated in suboceanic lithosphere of the Pacific plate. Lithospheric melting seemingly requires vertical flow of mantle material, although there is no direct evidence at the MEF for crustal extension that might provide a mechanism for mantle advection. In any case, most MEF magmas are subalkaline because of moderately high degrees of partial melting at shallow depth.

Alaska↗
USGS1994

Mineral-resource assessments in Alaska; background information to accompany maps and reports about the geology and undiscovered-mineral-resource potential of the Mount Katmai Quadrangle and adjacent parts of the Naknek and Afognak quadrangles, Alaska Peninsula

Geologic and geochemical field studies were carded out from 1983 to 1987 in the Mount Katmai l?x2 ? quadrangle and adjoining region, at the northeast end of the Alaska Peninsula. The region is nearly entirely within Katmai National Park and Preserve and has had almost no mineral production, so prior to this study there were few data by which to assess the mineral potential of the region. This report describes the folio of publications that have resulted from the study: geologic maps, geochemical results, fossil identifications, radiometric rock ages, and an assessment of the undiscovered-mineral-resource potential of the region. The Katmai region is inferred to potentially have three types of undiscovered mineral deposits: porphyry copper (molybdenum), precious-metal vein, and hot-springs gold. These deposit types occur elsewhere on the Alaska Peninsula in similar geologic units. Evidence suggesting their occurrence in the Katmai region is the presence of trace amounts of metals typically associated with these kinds of deposits in bedrock of certain tracts and in sediments of streams draining those tracts. Magma to provide heat, fractures to provide pathways for mineralizing fluids, and altered rock are required by genetic models of these deposit types. Such features do occur in the Katmai tracts. Confirmation of any mineral deposit in the Katmai region requires detailed follow-up sampling and acquisition of subsurface information, which is beyond the scope of this study. However, producing porphyry deposits are unknown elsewhere on the Alaska Peninsula in similar rocks, so if any such deposits occur in the Katmai region, they are likely to be few in number. Conversely, vein deposits are typically small in size so there may be several of such deposits. The properties and thermal history of the sedimentary rocks that could serve as reservoirs for oil or gas are unfavorable in adjacent regions. Thus the potential of the Katmai region for producible quantities of fossil fuels is low. In theory the region has shallow concentrations of geothermal fluids, but specific evidence for their presence is obscured by heavy precipitation and cold young rocks or deposits. Small volumes of coal occur at tidewater sites on the Pacific coast.

Circular↗
USGS1992

Mineral and energy resource assessment maps of the Mount Katmai, Naknek, and western Afognak quadrangles, Alaska

On the basis of new geologic mapping and exploration geochemical studies, we have provided a mineral and energy resource assessment of the Mount Katmai, Naknek, and western Afognak quadrangles, Alaska. We delineate four tracts of ground that have metallic mineral resources. The mineral deposit types considered in each tract are summarized in table 4. Estimates of the number of undiscovered mineral deposits have been made for porphyry copper and polymetallic vein deposits. We estimate that one undiscovered porphyry copper deposit is present in the Katmai study area at the ten percent probability level. Although the sampling density may be too low to give an accurate estimate of the number of undiscovered polymetallic vein deposits, we suggest that, at a minimum, there is a five percent probability for five or more undiscovered polymetallic vein deposits in the Katmai study area. In addition, several areas have potential for undiscovered porphyry molybdenum, massive sulfide, and epithermal gold and mercury deposits. Several placer gold claims have been filed in the area; one is still active. One claim, on American Creek, produced a small but unknown amount of gold. Several source areas for gold are identified in this study and would provide potential sources for gold in stream placer deposits given the right hydrologic conditions. Many of these sites in the Kulik Lake area have been prospected with only limited success. However, the upper reaches of lkagluik Creek and some areas of the Rainbow River in the central part of Katmai National Park may also contain undiscovered placer gold resources. Berryhill (1963) investigated the titanium-rich black sand beach placers along the coast of Bristol Bay at Egegik Bay and concluded that they did not constitute a resource for either titanium or gold. Sand and gravel deposits are locally abundant (Riehle and Detterman, in press) and are adequate to supply local demand. No cinder resources have been delineated. Energy potential evaluated during the study includes geothermal, oil and gas, and coal resources. A few warm springs were found, but no hot springs areas suitable for geothermal development exist within the study area. Better sites for geothermal resources have been identified on the Alaska Peninsula south of the study area (Smith and Shaw, 1975). The potential for commercial accumulations of oil and gas in the Naknek, Mount Katmai, and western Afognak quadrangles is low. Area E1, in the Naknek quadrangle along Bristol Bay, has low potential for thermogenic oil and gas (Church, Detterman, and Wilson, 1989). In area E2, oil seeps are along the anticlinal structures both north and south of the Katmai study area. Studies by Magoon and Anders (1992) indicate that the oil is from lower Mesozoic sedimentary rocks. Surface exposures of the Naknek Formation have uniformly indicated poor reservoir characteristics where studied, both here and in the adjacent quadrangles, and the shallow depth of burial of the Naknek Formation probably would result in flushing of the reservoir by meteoric water if oil were present. Coal seams as much as several meters in aggregate thickness crop out in Tertiary rocks in the Geographic Harbor area. Since these coal beds occur within withdrawn Federal lands, there has been no incentive to evaluate them as coal resources. Given different land accessibility and a local market, these beds could constitute a small marketable coal resource.

Alaska↗