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Introduction: the Map of the Area of Venus Lo- Cated Within 35 to 90° S, and 80 to 200° E Was Lunar and Planetary Science XXXI 1185.pdf LAIDAMLULUM VALLIS, THE THIRD LONGEST LAVA CHANNEL ON VENUS: DISCOVERY REPORT G.A.Burba Vernadsky Institute of Geochemistry and Analytical Chemistry, Russia’s Academy of Sciences, 19 Kosygin Str., Moscow 117975, Russia <[email protected]> Introduction: The map of the area of Venus lo- fornia. It is name of the Morning Star Woman, wife of cated within 35 to 90° S, and 80 to 200° E was com- Kuksu, the first man. The name from the culture of piled within the frames of VENGLOBGEK project on Californian people have been chosen to produce a link the global geologic mapping of Venus [1,2,3]. This with the Magellan mission, which was controlled with area, as the most of the Southern Venus, is known as the California-located facilities of the Deep Space the lowlands since the Pioneer Venus altimetric survey Communication Network and the Jet Propulsion Labo- in 1979. It was imaged for the first time with the Ma- ratory. gellan SAR in 1991-92. In the course of the mapping Geologic setting: The channel is located on the a very prominent, still unknown lava channel was find plain with wrinkle ridges, the geologic unit, which out. This feature belongs to canali type of Venus occupies the largest area on Venus. It looks the chan- channels [4,5]. nel was formed either simultaneously with the wrin- Location: The terminals of this new channel are kle-ridged plains emplacement, or just after it. The at 83.5°S, 160.0°E and 62.0°S, 142.5°E. The channel younger radar bright lava flows superpose the channel is located within Alma-Merghen and Imapinua Plani- near its southern end (Yagami Fluctus) as well as at tiae. It goes across Alma-Merghen Planitia northward the northern one (Nambubi Fluctus). - from the area between Whatitiri Corona* and Bick- Some comparisons: The six longest channels on erdyke crater, east of Yagami Fluctus*, to Shelikhova Venus, which have more than 1000 km in length are Patera (just west of it), crossing Odzerchen Dorsa* listed in Tabl. 1. east of Giliani, then goes across Tukwunag Dorsa to Imapinua Planitia. Here the channel still goes on Table 1. The longest channels on Venus northward – west of Melania to the eastern edge of Nambubi Fluctus – at the area SW of Blixen. (Aster- Feature name Length, km isked are preliminary names – those to be finally ap- proved by the International Astronomical Union – Baltis Vallis 6000 IAU – in August 2000 [6] ). It is necessary to note, Citlalpul Vallis 3160 that the area south of 83.5°S is not imaged, so the Laidamlulum Vallis 2700 channel may have southward extention. Koidutahet Vallis 1820 Size: The observable (i.e. north of 83.5°S) length Ikhwezi Vallis 1700 of the new channel is 2700 km. So, this feature is the Uottakh-sulus Valles 1100 third longest channel on Venus after Baltis Vallis (6000 km) and Citlalpul Vallis (3160 km). The wide One could see that Laidamlulum Vallis is very close in of the channel is about 1.5 km and it is very stable length to Citlalpul Vallis beeng 85% of the latter. But along the whole length of the channel. the next, Koidutahet Vallis, is only 67% from the Slope: It could be inferred that the channel have length of Laidamlulum Vallis. It could be of some northward downhill direction. Such conclusion is geologic meaning that second, third and fourth longest based mostly on the elevation data for the four neigh- channels on Venus (i.e. Citlalpul, Laidamlulum and bor craters – Bickerdyke, Giliani, Melania and Blixen. Koidutahet) are located in the same area within the Any geomorphic evidences of flow direction, such as southern hemisphere of the planet. Both Laidamlilum island configuration or passing of obstacles, were not and Koidutahet looks to originate from the same found on the images (FMAP). The elevation drop source region – Whatitiri Corona, but the absence of from the southern terminal of the channel to the images for the southern portion of Whatitiri prevents northern one was found to be 0.78 km. It means the to make a final conclusion on it. down gradient is 0.029%, or 1 minute of arc. Some terrestrial rivers to compare the down gra- Naming: On our request this new channel was dients with that of Laidamlulum Vallis are listed in named in 1999 by the IAU as Laidamlulum Vallis [6]. Tabl. 2. This is just to provide a clear view what down After the IAU rules the large valleys/channels are gradients look like for the known features, but not to named with the name of planet Venus in different compare lava flow with water one. The rivers of cultures. The name for this feature was chosen from nearly the same length as Laidamlulum Vallis have the mythology of Maidu, the ancient people of Cali- been chosen. Lunar and Planetary Science XXXI 1185.pdf NEW LONG LAVA CHANNEL, VENUS: G. A. Burba Table 2. Down gradients of some terrestrial rivers Name Length, km Elev. drop, km Gradient, % Danube 2860 0.75 0.026 Orinoco 2740 0.75 0.027 Ural 2430 0.63 0.026 Ganges 2700 5.5 0.20 Amudarya 2540 4.95 0.19 Colorado 2330 4 0.17 The first three rivers have nearly the same down gra- dient as Laidamlulum Vallis, i.e. their mean slope is 1 minute of arc. The latter three rivers were chosen to demonstrate the maximal values of gradients, which took place for the terrestrial rivers of nearly the same length as Laidamlulum Vallis is. The mean slopes in these cases are 6 to 7 minutes of arc. It could be useful to note that such river as Dnipro (Dnieper) with the length of 2200 km have 0.25 km elevation drop, and so its down gradient is as small as 0.01%, which is three times smaller than that of Laidamlulum Vallis. References: [1] Burba G.A., Basilevsky A.T. et al. (1998) 3rd Int. Conf. Explor. Utiliz. Moon (abstr.), 103. [2] Burba G.A., Shashkina V.P. et al. (2000) This volume. [3] Basilevsky A.T., Burba G.A. et al (1998) 3rd Int. Conf. Explor. Utiliz. Moon (abstr.), 108. [4] Baker V.R. et al. (1992) JGR, 97, No. E8, 13,421– 13,444. [5] Baker V.R. et al. (1997) in: Venus II, S.W.Bougher et al., eds., Univ. Ariz. Press, Tucson, 757. [6] Burba G.A., Blue J. et al. (2000) This volume..
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