Sif Mons
Sif Mons is an active shield volcano located in Eistla Regio on Venus. It has a diameter of and a height of. The volcano is one of the few identified active extraterrestrial volcanoes, having last erupted between 1990 and 1992. It is named after the Norse goddess Sif; the name Sif Mons was officially adopted by the International Astronomical Union in 1982.
Geology and characteristics
Sif Mons is a broad shield volcano with an approximate radius of ~1,000 km and a measured peak elevation of ~2.2 km. Sif Mons's slopes are very shallow, with a maximum slope on its southwestern flank of just 0.2° and a minimum slope on its northern flank of less than 0.04°. Sif Mons's peak is occupied by an unusually shallow or infilled circular summit caldera roughly 50 km in diameter. The caldera appears bright on radar imagery, with distinct lava flows radiating down the eastern flank. Small radar-dark regions under 50 km in diameter lie near the summit; the dark appearance in radar imagery may be due to smooth lava flows or smooth material not covered by other flows. The dark regions have irregular edges, indicating that they may be pyroclastic flow deposits. As the radar-dark regions follow Sif Mons's topography, planetary scientists Bruce A. Campbell and Donald B. Campbell interpreted the features as smooth lava flows.Additional subsidiary flows have been identified on Sif Mons's volcanic edifice, likely originating from independent eruptions from multiple vents. Other subsidiary features include an uplifted region ~1.7 km high to the southeast of Sif Mons and a volcanic cone 5–8 km in diameter to the north. The uplifted region is circular in profile, likely being a central vent for additional lava flows or a ring of small domes. The northern volcanic cone, meanwhile, is the source for a single major flow that extends down the flanks of Sif Mons for ~200 kilometers before continuing into southern Sedna Planitia.