Venusian Structure. Iron-Nickel rich core Mantle composed of magnesium-rich silicates and oxides Basaltic crust Venera 13 & 14 Tholeiitic basalt

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1 Vulcanism on Venus

2 Venusian Structure Iron-Nickel rich core Mantle composed of magnesium-rich silicates and oxides Basaltic crust Venera 13 & 14 Tholeiitic basalt

3 Tesserae From latin word for Tile Covers 10% of surface Result of crustal compression through tectonic activity This region covering an area of 37 by 80 km, located at 30N 333E on the low rise separating Sedna Planitia and Guinivere Planitia

4 Venus Surface

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7 Volcanic Structures Large Volcanoes Small Volcanoes Lava flows Lava Channels Calderas Coronae Novae Arachnoids The global distribution of volcanic features on Venus. NASA.

8 Shield Volcanoes More than 150 large shields Upland regions Gentle slopes, long radial flows Central vent or summit caldera The global distribution of large shield volcanoes on Venus. Each red triangle marks the site of a shield volcano over 100 km in size. NASA.

9 Sapas Mons, near the equator in Atla Regio Magellan Press Release Image P-38360, JPL image MGN-51 Ushas Mons, on the northern part of Dione Regio Magellan Press Release Image P-42386, JPL image MGN-117

10 Viscous, silicate rich lava flows ''pancake'' domes Little evidence of explosive eruptions High atmospheric pressure Water content in magma Volcanic 'pancake' domes in Tinatin Planitia, located at 15N, 9E. Nasa Chain of pancake domes east of Alpha Regio

11 Mostly in lower elevations and on the plains ''anemone'' shields Central vent, lava flows ''tick'' volcano Raised rim, radial ridges The global distribution of small shield volcanoes (ranging between 20 and 100 km across), small shield fields and volcanoes with anemone (flower-like) patterns of lava flow. NASA.

12 Venusian 'anemone' shield, 10S, 201E NASA Venusian 'tick' volcano, diameter 30 km 20S, 3E NASA

13 Cones Mainly circular, steep slopes Small groups on fractured plains A field of volcanic cones lies on the fractured plain of Niobe Planitia. These cones average 2 km wide and rise to heights of around 200 m. NASA.

14 Lava flows 80 % of lowland plains More than 50 Mostly around elevated borders of lowland plains Some show streamlined islands Mylitta Fluctus Streamlined islands in a lava outflow channel in the Ammavaru area, Lada Terra. NASA Mylitta Fluctus, a large volcanic flow field in Venus southern hemisphere. NASA.

15 Lava Channels In volcanic plains Similar to terrestrial rivers Due to surface temperature and pressure the lava stays fluid longer Baltis Vallis 6800 km long A 600 km long section of the Solar System s longest lava channel, Baltis Vallis. NASA. A lava channel some 200 km long and 2 km wide cuts through the terrain south of Atira Mons. NASA.

16 Calderas Large circular or elongated depression Formation process Sacajawea Patera (64N, 335E), an elliptical caldera measuring km. Its floor lies some 2,000 m beneath its rim. NASA.

17 Coronae Ø: km Circular or oval structures Complex fractures Formed because of rising molten rock Fotla Corona (59S, 164E), 150 km in diameter, displays a number of pancake volcanoes. NASA.

18 Arachnoids Concentric fracturing Strong radial faulting Concentric structures enclose radial faults => Spider-web Typical arachnoid feature, NASA

19 Novae Lack annular fractures Central dome Radial fracturing Early stage of corona formation This nova lies in Themis Regio at 30S, 279E and measures 250 km across. NASA.

20 Chronology of Corona and Nova Formation The proposed cases for corona-nova chronology. (Aittola et al., 2002)

21 Active Volcanism? Few impact craters => entire surface younger than ½ billion years Clouds of SO2 (volcanic gas) and many volcanoes no active volcanism detected Infrared observations indicate some regions were resurfaced rather recently. Venus was recently (and still may be) volcanically active. Radar and topography image from the Magellan spacecraft of Idunn Mons on Venus, which was recently volcanically active. Dark regions are smooth, and bright regions are rough or steep. Elevations have been exaggerated thirty times.

22 Surface Hot Spots Some volcanic regions have higher emissivity than their surroundings Lower emissivity regions have reacted chemically with CO2 and SO2 in the atmosphere, forming a thin crust over the lava High emissivity indicates younger material that has not been substantially weathered by Venus' thick atmosphere Infrared observations from the Venus Express spacecraft overlaid on the image from the previous slide show that Idunn Mons (red) has higher thermal emissivity than its surroundings (blue). This indicates a compositional difference between the two regions.

23 Sources Venus, Peter Cattermole Venus and Mercury, and How to Observe Them, Peter Grego Aittola et al. 2002, Chronology of the formation process of Venusian novae and the associated coronae Müller, Volcanic Structures at Venus