Glossary

Surface Effects: Terms, Definitions, and Acronyms

The following are commonly observed and mapped surface effects features at the Nevada Test Site. These definitions were compiled from a variety of sources including Allen and others, 1997; Garcia, 1997; Houser, 1970; Drellack, 1988; and Garcia, Drellack, and McKinnis, [unpublished data].

Collapse sink (or sink): A topographic depression caused by surface subsidence within the chimney above an underground nuclear detonation, at or near surface ground zero. Often informally referred to as a crater at the Nevada Test Site, collapse sinks are distinct from craters in that there is no throw-out or vaporization of surface materials.

Crack (or fracture): A break or parting of the ground surface caused by an explosion-induced mechanical failure of the geologic surface material. Cracks generally range from “hairline” to several tens of centimeters in width, and from several centimeters to several hundreds of meters in length. The largest cracks are usually associated with the highest-yield detonations and/or nearby faults (Allen and others, 1997, p. 29). In the context of surface effects mapping, a crack that has a limited vertical extent below the ground surface is referred to as a fracture. However, because this distinction was not made on the original surface effects maps, the words crack and fracture are used synonymously in this report. The following types of fractures (cracks) are present in Yucca Flat and Pahute Mesa.

• Concentric fracture: Surface fractures that form in a circular orientation around surface ground zero of an underground explosion.

• Hairline fracture: Surface fractures that have a width (aperture) of less than 3 mm. Hairline fractures tend to form on prepared surfaces, such as roads.

• Linear fracture: Surface fractures that form in a series (or trend) of discontinuous, en echelon, parallel, or sub-parallel linear features.

• Radial fracture: Surface fractures oriented in a “spoke-like” pattern around surface ground zero.

• Reactivated fracture: A pre-existing fracture on which failure recurs during a subsequent detonation.

• Random fracture: Small-scale movement along pre-existing block joints in the underlying rock or in the surface rock sometimes called “Block Chatter”. The results of these movements may appear random or in a mosaic pattern.

Crater: A topographic depression caused by an explosion at or near the surface that forms as a result of compaction, throw-out (ejecta), and/or vaporization of surface materials. The largest craters were produced in Yucca Flat and Pahute Mesa as the result of excavation experiments in the 1960’s under the Plowshare Program. These include the 1962 Sedan crater, located at the northern end of Yucca Flat, and the 1968 Schooner crater located in the northwest corner of Area 20 on Pahute Mesa.

Fault: An extensive fracture caused by an underground detonation along which vertical and/or horizontal displacement has occurred. Although a fault is commonly referred to in the singular, the largest faults of Yucca Flat and Pahute Mesa (e.g., Yucca Fault, Carpetbag Fault, and other named and unnamed faults) consist of several parallel, braided, and en echelon faults that form fault or fracture zones.

Pressure ridge: A low, narrow topographic ridge raised above the ground surface by compressional stresses resulting from an underground detonation. Pressure ridges are typically straight to slightly curved or locally sinuous.

Surface effect: A stress-induced surface feature caused by an underground nuclear detonation. Surface effects include cracks, fractures, faults, pressure ridges, and collapse sinks (or craters) that form as a result of an underground nuclear detonation. The surface expression of these features provides insight into the geological and structural nature of the nuclear testing area.

Surface Ground Zero (SGZ): That point on the ground surface that is located directly above an underground nuclear detonation.

Miscellaneous: Terms, Definitions, and Acronyms

ESRI (Environmental Systems Research Institute): Geographic Information Systems software company and developers of ArcView GIS (v. 3.2) and ArcGIS (v. 8.2) used in this project..

GIS (Geographic Information System): A set of tools and procedures for storing, retrieving, updating, analyzing, and displaying digital map data and attribute information.

GIS Theme, Map Layer, or Coverage: These terms are often used interchangeably to describe map overlay that is organized around some type of thematic information. They can contain point, line, or polygon information. A GIS roads theme, for example, would contain the digital vectors (lines) pertaining to the locations of roads, trails, and other transportation features and contain attribute (database) information about each individual line of the roads theme. A point theme would be used to demarcate a site, such as a nuclear test site, whereas a polygon theme would be used to delineate a map feature that has a set spatial extent, such as an Operational Area of the NTS. All GIS maps contain an attribute table that contains information about the spatial features.

NTS (Nevada Test Site): The Nevada Test Site is located in south-central Nevada.

NSP (Nevada State Plane) Coordinate System: The primary rectangular map coordinate system used in the GIS Surface Effects Maps Archive. The NSP coordinate system is based on the Universal Transform Mercator (UTM) projection and consists of three segments--west, central, and east. The NTS is in the central division. All maps displayed here are in the NSP (central, in feet) coordinate system unless otherwise noted.

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