Astronomy:Sif Mons

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Short description: Active shield volcano on Venus
Sif Mons
File:250px
False-color computer-generated view of Sif Mons, with height exaggerated
Feature typeShield volcano
LocationEistla Regio, Venus
Coordinates [ ⚑ ] : 22°00′N 7°36′W / 22.0°N 7.6°W / 22.0; -7.6[1]
Diameter210 km (main structure)
1 200 km (lava flow apron)[2]: 77 
Peak2 km (base-to-peak)[2]: 77 
EponymSif

Sif Mons is a large shield volcano located in western Eistla Regio, a highland region on Venus. Composed of a main volcanic structure surrounded by an outer apron of lava flows 1,200 kilometres (750 mi) in diameter, it rises about 2 kilometres (1.2 mi) from its base. It is one of a few extraterrestrial volcanoes where signs of ongoing volcanic activity have been observed, with candidate eruptions in 1990 and 1992. It is named after the Norse goddess Sif; the name Sif Mons was officially adopted by the International Astronomical Union (IAU) in 1982.[1]

Geography and morphology

Computer-generated view of Sif Mons (right) and Gula Mons (left). Height is exaggerated.

Sif Mons lies in western Eistla Regio,[2]: 77  a roughly 2,500-by-1,500-kilometre (1,550 mi × 930 mi) highland in Venus's northern hemisphere that rises 0.5–1.0 kilometre (0.31–0.62 mi) high.[3]: 16036  Sif Mons lies 750 kilometres (470 mi) to the west of the larger Gula Mons,[4]: 177  and together the two mountains dominate the center of western Eistla Regio.[5]: 1353 

Sif Mons is broad shield volcano[6]: 975  rising 2 kilometres (1.2 mi) from its base. It is composed of a central main structure 210 kilometres (130 mi) in diameter, surrounded by an outer apron of lava flows extending up to 600 kilometres (370 mi) from the center. The main structure has slopes of 1–3°, which drop to 0.15–0.25° in the outer flow apron; the main structure has a volume of about 1,600 cubic kilometres (380 cu mi).[2]: 77  Multiple figures have been given for the total diameter of the mountain, from several hundreds of kilometres[4]: 177 [7]: 13397  to a thousand kilometres.[5]: 1353  Its 40-kilometre (25 mi) diameter summit caldera is nearly circular, with a relatively flat and smooth floor. The caldera's southern rim is well-defined, but its lower northern rim is less distinct and appears as a series of lineaments, partly covered by caldera lava flows. The northern rim lies 200 metres (660 ft) below the southern rim, and the caldera itself is no more than several hundred metres deep. Nested groups of smaller calderas overlap the main caldera's northern and northeastern rims. The smaller calderas range from 1.5 to 6.5 kilometres (0.93 to 4.04 mi) in size, with the northeastern group partially flooded by lava from the main caldera. Chains of smaller pits 0.4–1.5 kilometres (0.25–0.93 mi) in size extend away from the southern main caldera rim to the southeast.[7]: 13404 [2]: 77 

Flank eruption sites are common around Sif Mons, which form small secondary structures on its slopes. Many of these flank structures are surrounded by flow deposits of their own; one northern cone's lava flow extends over 200 kilometres (120 mi) to the north into Sedna Planitia.[2]: 77 [5]: 1354  A system of fractures oriented radially from its center occupy most of its flanks; they are less prominent than the ones on Gula Mons. The fractures are best developed on Sif Mons's northwest flank, while being absent from the northeast.[3]: 16040  These fractures cross older lava flows, and some younger lava flows have been channelized through the fractures.[7]: 13402, 13404  To the east, lava flows from Sif Mons and Gula Mons meet. At this point, flows from Sif Mons divert to the northwest by the elevated Idem-Kuva and Nissaba coronae.[7]: 13406 

Geology

Possible volcanic activity

On 27 May 2024, a paper was published reporting evidence of ongoing volcanic activity at Sif Mons. Using synthetic-aperture radar (SAR) data collected during the Magellan spacecraft mission, the authors identified changes in radar backscatter on the flank of Sif Mons and across a western regions of Niobe Planitia. These changes, which took place between 1990 and 1992, are likely due to lava flows that erupted within the aforementioned timeframe. Alternative causes for the observed changes were ruled out; variations from different viewing angles were accounted for in the analysis, and the observed changes were inconsistent with dune fields observed elsewhere on Venus. The lava flows on Sif Mons occupy its western flank, flowing downslope and covering older flows. The lava flows are estimated to be roughly 30 km2 in area, comparable in size to flows erupted from the Kīlauea volcano in Hawaii during a 3-month eruption in 2018.[8][6]

References

  1. ↑ 1.0 1.1 "Sif Mons". Gazetteer of Planetary Nomenclature. USGS Astrogeology Research Program. (Center Latitude: 22.00°, Center Longitude: 352.40°; Planetocentric, +East)
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 Stofan, Ellen R.; Guest, John E.; Copp, Duncan L. (July 2001). "Development of Large Volcanoes on Venus: Constraints from Sif, Gula, and Kunapipi Montes". Icarus 152 (1): 75–95. doi:10.1006/icar.2001.6633. 
  3. ↑ 3.0 3.1 Grimm, Robert E.; Phillips, Roger J. (October 1992). "Anatomy of a Venusian Hot Spot: Geology, Gravity, and Mantle Dynamics of Eistla Regio". Journal of Geophysical Research 97 (E10): 16035–16054. doi:10.1029/92JE01500. 
  4. ↑ 4.0 4.1 Senske, D. A. (November 1991). "Geology and tectonics of Beta Regio, Guinevere Planitia, Sedna Planitia, and Western Eistla Regio, Venus: Results from Arecibo image data". Earth, Moon, and Planets 55: 163–214. doi:10.1007/BF00058901. ISSN 0167-9295. 
  5. ↑ 5.0 5.1 5.2 Campbell, Bruce A.; Campbell, Donald B. (August 1990). "Western Eisila Regio, Venus: Radar properties of volcanic deposits". Geophysical Research Letters 17 (9): 1353-1356. doi:10.1029/GL017i009p01353. Bibcode: 1990GeoRL..17.1353C. 
  6. ↑ 6.0 6.1 Sulcanese, Davide; Mitri, Giuseppe; Mastrogiuseppe, Marco (2024-05-27). "Evidence of ongoing volcanic activity on Venus revealed by Magellan radar" (in en). Nature Astronomy: 1–10. doi:10.1038/s41550-024-02272-1. ISSN 2397-3366. https://www.nature.com/articles/s41550-024-02272-1. 
  7. ↑ 7.0 7.1 7.2 7.3 Senske, D. A.; Schaber, G. G.; Stofan, E. R. (August 1992). "Regional topographic rises on Venus – Geology of Western Eistla Regio and comparison to Beta Regio and Atla Regio". Journal of Geophysical Research 97 (E8): 13395–13420. doi:10.1029/92JE01167. ISSN 0148-0227. 
  8. ↑ Andrews, Robin George (2024-05-27). "Rivers of Lava on Venus Reveal a More Volcanically Active Planet" (in en-US). The New York Times. ISSN 0362-4331. https://www.nytimes.com/2024/05/27/science/venus-volcanoes-lava.html. 



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