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H. A. Pohn

Publications and source records attributed to H. A. Pohn.

11 recordsLinked to original sources
USGS1991

Fold patterns, lateral ramps and seismicity in central Pennsylvania

The Susquehanna lateral ramp crosses the entire length of Pennsylvania in a NNE direction and extends into southern New York State. Its presence was first suspected because of a dramatic change in fold wavelength across the Susquehanna River, seen on both side-looking airborne radar (SLAR *) data and the geologic map of Pennsylvania. Seismic reflection profiles confirm the presence of a ramp and show the detailed nature of structures associated with it. These structures include antiformal stacks, juxtaposed anticlines and synclines, and folds beheaded by thrust faults. The change in the fold pattern, which led to recognizing the lateral ramp, occurs above a rapid dropoff in depth to the basement suggesting that the ramp and the basement configuration may somehow be related. In plain view, eleven earthquakes are spatially related to the Susquehanna lateral ramp, although they are in the basement rocks rather than in the cover rocks which contain the lateral ramp itself. The earthquakes are, therefore, not likely directly associated with the ramp, though they may be affiliated with strike-slip faulting in the basement which, itself, appears to be partly responsible for the formation of the ramp. The initial age of the faulting along, and in the vicinity of, the Susquehanna lateral ramp is presumably Early to Middle Paleozoic. However, the presence of a surficially-exposed Mesozoic dike along the ramp and modern seismicity suggest that the Susquehanna lateral ramp may be a zone of protracted, and perhaps repeated, tectonism which is currently being reactivated. A preliminary evaluation of the distribution of modern earthquakes in the Valley and Ridge, Blue Ridge and Appalachian Plateau shows that nearly half of the earthquakes are located under lateral ramps. If this observation is true, the presence of ramps may be a useful geological indicator of areas susceptible to seismicity.

Pennsylvania↗
USGS1983

The relationship of joints and stream drainage in flat-lying rocks of south-central New York and northern Pennsylvania

Examination of the relationship of joints to stream development shows that the oft-cited development of streams parallel to joint directions does not, in general, apply in south-central New York and adjacent northern Pennsylvania. Streams whose courses are oblique to the joint directions (joint-oblique valleys) tend to erode easily owing to increased corrasion and subsequent undercutting at the upstream intersection of joints. The removal of joint-bounded blocks in joint-oblique valleys forms cascades that advance headward by apical erosion. Streams whose courses are parallel and perpendicular (joint-parallel valleys) to the nearly orthogonal joint sets erode by waterfall and plunge-pool formation; bedrock is undercut on the downstream side, and unstable blocks subsequently collapse into the plunge pool. Most valleys in the Finger Lakes region are joint-oblique, although some well-developed valleys are joint-parallel. These joint-parallel valleys are usually due to (1) a single deep, pervasive joint whose presence acts as a barrier to lateral expansion of the stream, or (2) erosion along joint zones whose intense fracturing produces weak erosional resistance in the rocks.

New York, Pennsylvania↗
USGS1982

Evaulation of remote sensing, geological and geophysical data for south-central New York and northern Pennsylvania

A study was made of the relationship between lineaments observed on Landsat satellite images and the geologic framework of a portion of the Allegheny Plateau of south-central New York and northern Pennsylvania. The area is underlain by a relatively thick sequence of salt and other evaporites in the Silurian Salina Group and is a potential site for deep-storage of solid nuclear waste. A combination of remote sensing techniques, detailed geologic mapping and geophysical investigations were applied to the problem. Because of the premature termination of the Department of Energy contract, only a portion of the total work was completed. The completed portion of the project included 1) digital contrast enhancement of several Landsat multispectral scanner (MSS) images, 2) analysis of lineament patterns from a Landsat MSS-7 mosaic, 3) field mapping of bedrock joint patterns, 4) compilation and analysis of surface and subsurface structure and isopach maps, 5) collection and digital analysis of aeromagnetic data for southern New York, 6) compilation and analysis of aeromagnetic and gravity data for much of New York and Pennsylvania, and 7) analysis of seismic reflection survey lines for selected portions of New York and Pennsylvania. We identified eight major lineaments or lineament zones and studied them in detail. They typically represent linear alignments of the most conspicuous or prominent physiographic features observable on Landsat images. The Cortland-Ithaca, Watkins Glen-Tanghannock, Seneca Lake-Elmira, Painted Post-Blossburg and Endicott-Syracuse conspicuous lineaments include the Corning-Bath, Van Etten-Towanda, Van Etten-Candor and Van Etten-Odessa lineaments. In addition, a major fault system--the West Danby fault zone--was further defined by geologic and geophysical investigations during our study; the fault zone was not recognizable on satellite images. The lineaments and lineament zones were categorized by their azimuthal trends. Those with a northerly orientation (e.g. Van Etten-Towanda, Seneca Lake-Elmira, Painted Post-Blossburg and Endicott-Syracuse) are most common. Northeasterly lineaments (e.g. Cortland-Ithaca and Watkins Glen-Taughannock) also are common. The Corning-Bath and Van Etten-Odessa lineaments have a northwesterly orientation and the Van Etten-Candor lineament is the sole representative of the east-west direction. The West Danby fault system also trends east-west. All the lineaments or lineament zones studied appear to be related, in one fashion or another, to structural disturbances, because changes in the structural attitude of beds or thickness of rocks commonly occur along their extent. The changes in many instances occur on multiple stratigraphic horizons and in a manner suggestive of several different styles of tectonism, leading to the conclusion that the lineaments and lineament zones have been periodically reactivated during the Paleozoic and Mesozoic Eras. Aeromagnetic data commonly show a parallel alignment of contours juxtaposed or on line with lineaments and lineament zones, suggesting that these physiographic alignments owe their origin to features within the crystalline basement. Pre-Alleghanian faulting and depositional patterns show that the study area was affected by basement-controlled adjustments along and in the same direction as most of the lineaments and lineament zones. Actual displacements cannot be proven for all of the lineaments or lineament zones, but changes in dip of the rocks across these features suggest either basement hingelines or small displacement faulting which cannot be resolved by the present data. These displacements occurred in at least Middle-Late Ordovician, Middle-Late Silurian and the Early-Middle Devonian times. The major northeast trending lineament zones (Cortland-Ithaca and Watkins Glen-Taughannock) correspond in orientation and lie along the northeastward projection of the Rome Trough, a postulated Paleozoic aulacogen. Results of

Open-File Report↗
USGS1974

Thermal inertia mapping from satellite – Discrimination of geologic units in Oman

The Nimbus III and IV satellites provide reflectance and emittance data from the earth's surface at 8-km resolution. These data have been used to derive a physical property of geologic materials termed '"thermal inertia" which appears to have great promise for discriminating surficial units. A thermal inertia map of part of Oman was produced from the Nimbus satellite measurements. Correlation of this map with a reconnaissance geologic map showed gross agreement with the major units but also suggested the need for some modifications of the reconnaissance map. Some of the anomalies were verified by comparison with a later, more detailed map; others remain unexplained and may indicate previously undiscriminated geologic units.

Journal of Research of the U.S. Geological Survey↗
USGS1972

Geologic map of the Tycho Quadrangle of the Moon

The Tycho quadrangle is centrally located in the southern half of the earthside hemisphere of the Moon. The area is characterized by a high density of craters, the largest of which – Stofler – is about 140 km in diameter. The northern and eastern parts if the quadrangle are dominated by plains ( pIp , Ip ) and hilly terra ( IpIt ) units of regional extent , and the western part by the crater Tycho and its ejecta blanket. Structural features probably associated with the Imbrium basin to the north and Orienta le and Humorum basins to the northwest are present, although blanketing units related to these basins are not recognized.

IMAP↗
USGS1972

Geologic map of the Macrobius Quadrangle of the Moon

The Macrobius quadrangle is in the northeast quadrant of the Moon’s near side. Although predominantly a highland area centered around the Taurus Mountains (Montes Taurus) , it is bounded by three major mare-filled basins: Tranquillitatis , the oldest, to the south; Seren itatis to the west; and Crisium on the east. Most of the geologic units within the quadrangle have been profoundly affected by the forma tion of these basins and by that of the younger Imbrium basin farther to the northwest. Some of the youngest material on the Moon, believed to be of volcanic origin, blanke ts part of the mare and terra along the southwest margin of the map. Sampling this material will be a primary objective of the Apollo 17 mission, whose proposed landing site is approximately at lat. 20 ˚ 10’ N ., long. 30 ˚ 45’ E. near the western edge of the map area.

IMAP↗
USGS1971

Geologic map of the Lansberg P region of the Moon Lunar Orbiter Site III P-9, Oceanus Procellarum including Apollo landing site 7 (Apollo 12)

The Lansberg P region lies within a lowland area between Mare Cognit um and the main part of Oceanus Procellarum , about 135 km due south of the crater Reinhold. The Apollo 12 landing site is in the west-central part of the region and has been mapped in detail by Cannon (1969) . Although the entire region is covered by cratered and rayed mare materials, the mare is almost entirely surrounded by the terrae and is probably relatively thin . Superposed on the mare are two rays from the crater Copernicus, many individual craters, and crater clusters.

IMAP↗
USGS1970

Remote Sensor Application Studies Progress Report, July L, 1968 to June 30, 1969. Controlled Field Experiments

Field Sites have been selected for controlled experiments to analyze physical and chemical parameters affecting the response of electromagnetic radiation to geological materials. Considerations in the selection of the sites are the availability of good exposures of nearly monomineralic rocks, level of geologic understanding, and ease of access. Seven sites, where work is underway or planned, contain extensive outcrops of the following rocks: stanstone, limestone, dolomite, and gypsum. Field measurement of quartz have been conducted at four sites.

Report↗