app.a

NASA SP-441: VIKING ORBITER VIEWS OF MARS

- APPENDIX I -

GLOSSARY

Aeolian.-A term applied to wind erosion or deposition of surface materials.

Albedo.-The reflectivity of a body compared with that of a perfectly diffusing surface at the same distance from the Sun, and normal to the incident radiation.

Apoapsis.-That point in an orbit farthest from the center of attraction.

Barchan.-A moving, isolated, crescent-shaped dune. The convex surface points toward the wind.

Basalt.-A dark, fine-grained volcanic rock. Very common.

Bench.-A small terrace or step-like ledge breaking the continuity of a slope.

Caldera.-A large volcanic depression containing volcanic vents.

Catena-Crater Chain. A chain or line of craters.

Cavitation.-Plucking of material from the floor of a channel caused by the sharply reduced pressures associated with extreme flow velocities.

Chaotic terrain.-A surface consisting of short, jumbled ridges and valleys.

Chasma-Canyon. An elongated, steep-sided depression.

Chondrite.-A stony meteorite characterized by chondrules embedded in a finely crystalline matrix consisting of orthopyroxene, olivine, and nickel-iron, with or without glass.

Collapse pit.-A closed, rimless depression caused by subsidence.

Dike.-A near vertical, planar, volcanic intrusion.

Dorsum (Dorsa).-Ridge(s). Irregular, elongate prominence.

Ejecta.-Material thrown out of an impact crater during formation. Such material may be distributed around a crater in distinctive patterns forming "ejecta rays" or "ejecta loops. "

Escarpment.-A long, more or less continuous cliff or relatively steep slope produced by erosion or faulting. See "scarp.'

Esker.-A long, low, narrow, sinuous, steep-sided ridge or mound composed of irregularly stratified sand and gravel that was deposited by a subglacial or englacial stream flowing between ice walls or in an ice tunnel of a continuously retreating glacier, left behind when the ice melted.

Etch pit.-A surface depression caused by the preferential removal of less resistant material.

Fault.-A surface or zone of rock fracture along which there has been displacement, from a few centimeters to a few kilometers in scale.

Folding.-The curving or bending of a planar structure such as rock strata, foliation, or cleavage by deformation.
Fossa (Fossae).-pitches. Long, narrow, shallow depression. They generally occur in groups and are straight or curved.

Fretted.-Eroded in such a manner as to produce two horizontal planar surfaces separated by near vertical escarpments.

Fretted channel.-Long, relatively wide, flat floored valley with tributaries. Mass wasting probably played a significant role in their formation.

Gelifluction.-Creep of frozen material.

Glacioaeolian.- Material remove d from a glacier by wind erosion.

Graben.-An elongate, relatively depressed crustal unit or block that is bounded by faults on its long sides.

Gradation.-The leveling of the< land, or the bringing of a land surface or area to a uniform or nearly uniform grade or slope through erosion, transportation, and deposition.

Inclination.-The angle between the plane of an orbit and a reference plane. The Mars equator is here used as the reference when referring to spacecraft inclination.

Interfluve.- Lying between streams.

Labyrinthus.- Valley complex. Complex, intersecting valleys.

Laminated terrain.-A surface made of layers of different types of materials: layered terrain.

Lava.-Rock from a volcano, generally molten when ejected.

Limb.-The outer edge of a planetary disk.

Lithosphere.-The solid outer portion of a planet.

Mare. - Low-lying, level, relatively smooth, plains-like areas of considerable extent.

Mass wasting.-A term that includes all processing by which soil and rock materials fail and are transported downslope predominantly en masse by the direct application of gravitational body stresses.

Mensa (Mensae). - Mesas. Flat topped prominence with cliff-like edges.

Mons (Montes).-Mountains. A large topographic prominence or chain of elevations.

Normal fault.-A break in the surface caused by tensional forces.

Orographie.-Pertaining to mountains, e specially in regard to their location and distribution.

Outflow channel.-A large-scale channel that starts at full width in chaotic terrain and has few, it any, tributaries.

Overthrusting.-A low-angle thrust fault of large scale, generally measured in kilometers.

Pahoehoe.-A type of lava having a glassy, smooth, and billowy or undulating surface; it is characteristic of Hawaiian lava.

Patera.-Irregular crater or a complex one with scalloped edges.

Pedestal crater.-A crater around which less resistant material has been removed from the ejecta leaving an elevated surface of more resistant ejecta material.

Periapsis.-The orbital point nearest the center of attraction.

Periglacial.- Said of the processes, conditions, areas, climates, and topographic features at the immediate margins of former and existing glaciers and ice sheets, and influenced by the cold temperature of the ice.

Perihelion.-That point in the orbit of a planet when it is closest to the Sun.

Phase angle.-The angle between a line from the Sun to the center of a body and a line from the spacecraft to the center of the same body.

Planitia-Plain. Smooth low area.

Planum.-Plateau. Smooth elevated area.
Pleistocene.-A recent geologic epoch of the Quaternary period beginning approximately one million years ago? the last glacial age.

Polygonal ground.-Patterned ground marked by polygon-like arrangements of rock or soil. Generally produced on Earth by ice-wedge polygons.

Precessing ellipse.-An ellipse in which the pole is changing direction.

Rampart.-A narrow, wall-like ridge.

Regolith.-A general term for loose material overlying bedrock.

Reverse fault.-See thrust fault.

Rift.-A narrow cleft, fissure, or other opening in rock (as in limestone), made by cracking or splitting.

Rille.-Relatively long, trench-like valley; has relatively steep walls and usually flat bottoms.

Runoff channel.-Relatively small channel probably caused by water erosion over a long period.

Scabland.-Elevated, essentially flat basalt-covered land with only a thin soil cover.

Scarp.-A line of cliffs produced form of escarpment, and the by faulting or by erosion. The term is an abbreviated two terms commonly have the same meaning, although "scarp" is more often applied to cliffs formed by faulting.

Sediment.-Solid, fragmental material or mass of such material originating from the weathering of rocks, e.g., sand, gravel, mud, alluvium.

Shield volcano.-A broad, gently sloping volcano.

Striae.-Striped ground.

Subduction zone.-An elongate region in which a crustal mass descends below another crustal mass.

Subsidence.-A localized gradual downward settling or sinking of a surface with little or no horizontal movement.

Tectonic.-A term pertaining to deformation of a planet's crust, especially the rock structure and surface forms that result.

Terminator.-An imaginary, diffuse line separating the illuminated and dark portions of a celestial body. There are two terminators: morning and evening.

Thermokarst.-Rimless depressions caused by the melting of ice and subsequent collapse of the surface.

Tholus.-Hill. Isolated comical small mountain or hill.

Thrust fault.-A fault caused by compressional forces.

Transcurrent faulting.-A large-scale strike-slip fault in which the fault surface is steeply inclined.

Troposphere.-The lowest layer in an atmosphere, generally considered to be 10-20 km thick.

Tuff.-Volcanic ash, particles of 4 mm diameter or smaller.

UTC.-Universal Time Coordinated.

Unconformity.-The relationship where the younger upper strata do not follow the dip and strike of older underlying strata.

Vallis (Valles).-Valley. A sinuous channel, many with tributaries. These are named "Mars" in many languages, e.g., Al Qahira Vallis is derived from the Arabic word for Mars.

Vastitas.-Extensive plain.

Yardang.-Elongated, sculpted ridge formed by wind erosion.

SOURCES

American Geological Institute: Glossary of Geology, 1972.
Robert J. Foster: Physical Geology. Charles E. Merrill Publishing Co., Columbus, Ohio, 1971.
Richard M. Pearl: Geology. Barnes & Noble, Inc., New York, NY, 1969.
G. DeVaucouleurs, et al.: "The New Martian Nomenclature of the International Astronomical Union, " Icarus 26, 85-98, 1975.