Bell Regio, Venus: Integration of remote sensing data and terrestrial analogs for geologic analysis

Abstract

Abstract. The geology and surface morphology of Bell Regio (18-42" N, 32-58'' E) are investigated using a combination of Magellan, Venera, and analogous terrestrial data. The properties of surface units are compared to either direct terrestrial analog measurements or to the behaviors predicted by theoretical models. Five major volcanic sources are identified from geologic mapping (Tepev Mons, Neferiiti corona, a large shield volcano east of Tepev, and two small edifices southeast of Tepev). The volcano Api Mons lies northeast of the main Bell uplift. The oldest volcanic units are associated with an extensive low shield volcano east of Tepev Mons and a small edifice southeast of Tepev. The annular flow apron of Tcpcv Mons formed next, with volcanism at a second small edifice on the southeast flank of Tepev Mons producing tlie youngest flow units. Comparisons between Magellan data, tenrestrial radar images, and field topography profiles suggest that only three units resemble terrestrial a'a flows; the remainder are consistent witli smoother paJioehoe-lype surfaces. This suggests that most of the flow units were erupted at relatively low volume effusion rates (<iOO mVs) over long periods of time or had very low viscosities. One flow unit has a knobby texture which resembles large tumuli or ridge stractures. Much of the tectonic deformation in the area is in the form of fractiures circumferential to the edifices and isolated blocks of tessera terrain; there are no rift zones such as those which occur at Beta Regio, Atla Regio, or Western Eistia Regio. Tepev Mons is characterized by very steep slopes (up to 40° along the east flank), a reladvely flat summit, and two large (11 and 31 km) calderas. Though covered in places by high-dielectric material, the Tepev Mons summit area is relatively smooth with the exception of annular rough deposits which ring the two calderas. These calderas are quite shallow (on the order of a few hundred meters at most), with no discernible difference hi radius between individual altimeter foolprinls inside and outside the larger eastern feature. Magellan and Venera data suggest that (he eastern caldera is covered by a layer of unconsolidated material. Ejecta from Miriam crater lias produced a halo with a dielectric constant of 6-7 surrounding Nefertiti corona, and Potanina crEUer éjecta is the likely source material for radar-dark wind streaks south of Tepev Mons. A low-dielectric (E=2-3) triangular region on the south flank of Tepev Mons may be a pyroclaslic or cratar éjecta deposit which has been spread westward by the wind. This region has undergone a wide variety of volcanic processes, with a major shift in emptive style from the older low-relief eastern volcanic center to the steep slopes and large summit calderas characteristic of Tepev Mons and the two smaller edifices.

Development of Large Volcanoes on Venus: Constraints from Sif, Gula, and Kunapipi Montes

“…All three volcanoes exhibit some degree of radial fracturing; none have concentric fractures such as those seen at volcanoes in the Galapagos (McBirney and Williams 1969). None of the volcanoes have near-summit diffuse deposits suggestive of pyroclastic activity, as seen at Ushas Mons (Keddie and Head, 1995), volcanoes in Bell Regio (Campbell and Rogers 1994), and volcanoes in central Eistla Regio (McGill 1994).…”

“…Quantitative analysis has shown that only a few of the brightest flows in venusian flow fields have roughnesses analogous to terrestrial aa (e.g., Campbell 1992, Campbell andRogers 1994). Rougher flows on Venus can be interpreted as block lavas where a thick crust has been broken during flow, fragmented pahoehoe where continued movement of the flow has broken up the crust, or true aa produced from volatile-rich eruptions.…”

Explosive volcanic activity on Venus: The roles of volatile contribution, degassing, and external environment

“…Lava flows have been recognised globally, while pyroclastic density currents and fallout deposits are apparently rare or absent. It has proved difficult to determine the nature of these less common volcanic deposits seen in the radar imagery of Venus and confirmation of an explosive origin has so far mostly proved to be controversial (Campbell and Rogers, 1994;Grosfils et al, 2011;Keddie and Head, 1995;McGill, 2000). One recent exception is a proposed pyroclastic deposit known as Scathach Fluctus, identified by Ghail and Wilson (2013).…”

Pahoehoe toe dimensions, morphology, and branching relationships at Mauna Ulu, Kilauea Volcano, Hawai'i

“…Submersible studies of the sea floor illustrate that submarine lava flows exhibit a range of morphologic properties similar to those of subaerial pahoehoe (Ballard et al 1979;Fox et al 1988;Gregg and Fink 1995). Furthermore, recent analyses of lava flow margins (Bruno et al 1992(Bruno et al , 1994 and radar backscatter properties (Campbell and Rogers 1994) suggest that pahoehoe flows can be identified on other planetary surfaces.…”