A region‐by‐region condensed description of almost all of the area that was radar‐photographed by Veneras 15 and 16 is presented. Using some generalizations, the diversity of terrain was reduced to a discrete set from which a geological‐morphological map was constructed. The predominant type of terrain of the studied area is a plain that was tentatively subdivided into five morphological types: ridge‐and‐band, patchy rolling plain, dome‐and‐butte plain, smooth plain, and high smooth plain. Stratigraphically, the ridge‐and‐band plains are the oldest and the smooth plains are the youngest. The stratigraphic position of the other types is yet to be determined. Large sections of the plains show similarities to the mare‐type basaltic plains of the moon, Mercury, and Mars. Other types of terrain are combinations of ridges and grooves in various patterns: linear parallel, orthogonal, diagonal or chevron‐like, and chaotic. In some places the ridge‐and‐groove terrain is Stratigraphically below the plain material, but in other places it appears to be plain material that has been subsequently deformed. Near the eastern and western boundaries of Ishtar Terra large (several hundred kilometers in diameter) ring‐like features can be seen that are named coronae or ovoids. Evidence of tectonic deformation and the presence of flow‐like patterns support their designation as volcano‐tectonic features. Beta Regio seems to be an uplifted plain showing evidence of rifting and volcanism. All types of terrain are sparesely peppered with craters of obvious impact morphology. Their average density gives the plain an age range of 0.5 to 1×109 years. The fact that many impact craters are still in the pristine state indicates a very low rate of surface reworking, at least for the last 0.5 to 1×109 years. No evidence for water‐erosion‐sedimentation processes has been found. The tectonic activity of Venus has no equivalent on the moon, Mercury, or even Mars, and can be compared only with that of the Earth. Intensive horizontal deformation, previously known only on Earth, occurs on Venus, but in a characteristic Venusian style.

A study of the composition, structure, and properties of Venusian rocks was carried out by Venera 13 and Venera 14. The main structural‐morphological types of provinces of the Venus surface were chosen for the study. The chemical and mineralogical composition of the rock at the Venera 13 landing site shows that it belongs to a group of weakly differentiated melanocratic alkaline gabbroids; at the Venera 14 landing site, the rock is similar to oceanic tholeiitic basalts. A most interesting property of the surface rocks is the great number of the strata that were visible in panoramas of the landing sites. Measurements of their physical and mechanical properties show that Venusian rocks have friable, weakly cemented porous structures. Analysis of information from Venera 8, 9, 10, 13 and 14 led to the conclusion that the most likely global process responsible for the formation of the present rock is volcanic eruption. Moreover, due to the high gas content of basaltic melts, eruptions are of an explosive character leading to the formation of pyroclastic rocks. Summing up data obtained by Venera enabled us to compare Venus with the earth, Mars, and the moon, to point out some regular global features in the evolution of these bodies, and to suggest some new problems for investigation.

Multispectral images of the basaltic surface of Venus obtained by Venera 13 were processed to remove the effects of orange-colored incident radiation resulting from interactions with the thick Venusian atmosphere. At visible wavelengths the surface of Venus appears dark and without significant color. High-temperature laboratory reflectance spectra of basaltic materials indicate that these results are consistent with mineral assemblages bearing either ferric or ferrous iron. A high reflectance in the near-infrared region observed at neighboring Venera 9 and 10 sites, however, suggests that the basaltic surface material contains ferric minerals and thus may be relatively oxidized.

Physico‐chemical modeling of the atmospheric‐lithospheric interaction on Venus is presented. The thermodynamic assessment is carried out in terms of Venera 11 and 12 and Pioneer Venus measurements and the dynamic atmospheric structure. The subcloud atmosphere is interpreted to be a zone of nonequilibrium chemical conditions while the near‐surface layer is presumed to be an equilibrium zone due to catalytic effects and low wind velocities. The mineral assemblages of the ‘weathering crust’ are calculated. The pyrite‐anhydrite‐magnetite assemblage is suggested as the buffering system resulting in reducing conditions (P02≈ 10−21 atm). The existence of hydration is problematic and is thermodynamically conceivable only for the sulfur enrichment of primary rocks (about 2 wt. %). The carbonate minerals are suggested to be unstable.

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