K. R. Blasius

Stratigraphic relationships within Martian polar cap deposits

Abstract Deposits of layered ice and dust accumulate on the smooth and banded terrains of the north and south polar cap deposits, while erosion of equator-facing slopes of layered terrain expose these layers. Banded terrain occurs at exposures of irregular layers resulting from slight erosion of the feather edges of layers deposited on pole-facing trough walls. These deposits unconformably overlap onto adjacent layered terrain. Stripping of layers occurs in areas of strong, multidirectional wind, forming striped terrain . Local wind scour has also produced steep scarps with crescentic planform, often associated with dune fields positioned immediately downwind. Unconformities are common within layered deposits in areas of complex topography at the north pole. These indicate that episodes of deposition of 5–10 layers alternate with slight erosion of pole-facing trough walls. Troughs that strike north-south alternate between erosional widening and deepening and depositional infilling, creating multiple unconformities. Troughs near the equatorward limit of polar deposits increase in relief by deposition on adjacent smooth terrain and, locally, by erosional deepening. Troughs may migrate poleward, replacing the relief increase by depositional infilling when they near the poles.

North Polar Region of Mars: Imaging Results from Viking 2

During October 1976, the Viking 2 orbiter acquired approximately 700 high-resolution images of the north polar region of Mars. These images confirm the existence at the north pole of extensive layered deposits largely covered over with deposits of perennial ice. An unconformity within the layered deposits suggests a complex history of climate change during their time of deposition. A pole-girdling accumulation of dunes composed of very dark materials is revealed for the first time by the Viking cameras. The entire region is devoid of fresh impact craters. Rapid rates of erosion or deposition are implied. A scenario for polar geological evolution, involving two types of climate change, is proposed.

Preliminary results from the Viking orbiter imaging experiment

During its first 30 orbits around Mars, the Viking orbiter took approximately 1000 photographic frames of the surface of Mars with resolutions that ranged from 100 meters to a little more than 1 kilometer. Most were of potential landing sites in Chryse Planitia and Cydonia and near Capri Chasma. Contiguous high-resolution coverage in these areas has led to an increased understanding of surface processes, particularly cratering, fluvial, and mass-wasting phenomena. Most of the surfaces examined appear relatively old, channel features abound, and a variety of features suggestive of permafrost have been identified. The ejecta patterns around large craters imply that fluid flow of ejecta occurred after ballistic deposition. Variable features in the photographed area appear to have changed little since observed 5 years ago from Mariner 9. A variety of atmospheric phenomena were observed, including diffuse morning hazes, both stationary and moving discrete white clouds, and wave clouds covering extensive areas.

Topography and stratigraphy of Martian polar layered deposits

Abstract Topography and stratigraphy of young sediments in the Martian north polar region are being studied from high-resolution Viking Orbiter images to test and constrain theories of terrain evolution driven by cyclical climate change. Several steepened slopes upon which layers are exposed in section were found to have local relief of 200 to 800 m and slopes ranging from 1 to 8°. First attempts to calculate average layer thicknesses from portions of sections yielded results ranging from 14 to 46 m, linearly correlated with slope. In some cases, under the assumption of short-range lateral continuity, a greater number of layers was inferred to be present than was actually resolved on a particular section. When apparent layer thickness are revised accordingly, the correlation with slope is destroyed. We conclude that images of the shallowest-sloping sections of layered deposits should yield the most stratigraphic information, and layers thinner than 14 m may occur; indeed, they may even be common or typical. Because of the sensitivity of summer frost distribution to local slope and other properties of exposed strata, interseasonal comparisons of images promise to enhance the capability to detect layers and differentiate them by material properties.

Photoclinometric determination of the topography of the Martian north polar cap

Abstract Photoclinometry is useful for the determination of topography for areas which have a uniform albedo. The technique is applied to early spring Viking images of the Martian north polar cap, taken when the surface was covered by a nearly uniform frost cover. Unlike earlier approaches, the topographic profiling can be used for surfaces with any photometric function, but the strike of the planetary surface relative to the illumination angle must be specified along the profile. The resultant profiles are relatively insensitive to misestimation of the photometric functin and slope orientation, but are quite sensitive to the assumed values of the reflectance of an equivalent level surface and the atmospheric opacity (if it is large).

Topography of Martian central volcanoes

Abstract New topographic maps of six large central volcanoes on Mars are presented and discussed. These features are Olympus Mons, Elysium Mons, Albor Tholus, Ceraunius Tholus, Uranius Tholus, and Uranius Patera. Olympus Mons has the general form of a terrestrial basaltic shield constructed almost entirely from lava flows; but with 20 to 23 km of relief it is far larger. Flank slopes average about 4°. A nominal density calculated from the shield volume and the local free-air gravity anomaly is so high that anomalously dense lithosphere probably underlies the shield. Uranius Patera is a similar feature of much lower present relief, about 2 km, but its lower flanks have been buried by later lava flood deposits. Elysium Mons has about 13 km of local relief and average slopes of 4.4°, not significantly steeper than those of Olympus Mons. Its upper flank slopes are significantly steeper than those of Olympus Mons. We suggest Elysium Mons is a shield volcano modified and steepened by a terminal phase of mixed volcanic activity. Alternatively, the volcano may be a composite cone. Albor Tholus is a partially buried 3-km-tall shield-like construct. Ceranius and Uranius Tholus are steeper cone-like features with relief of about 6 and 2 km, respectively. Slopes are within the normal range for terrestrial basaltic shields, however, and topographic and morphologic data indicate burial of lower flanks by plains forming lavas. These cones may be lava shield constructs modified by a terminal stage of explosive activity which created striking radial patterns of flank channels. Differences among these six volcanoes in flank slopes and surface morphology may be primarily consequences of different terminal phases of volcanic activity, which added little to the volume of any construct, and burial of shallow lower flanks by later geologic events. Additional topographic data for Olympus Mons, Arsia Mons, and Hadriaca Patera are described. The digital techniques used to extract topographiv data from Viking Orbiter stereo images are also described.