Lunar and Planetary Science XLVIII (2017) 2603.pdf

The Diverse Channel Networks of Juventae Chasma, Mars. Pragya Singh1, Ranjan Sarkar1, Alok Porwal1, Binita Phartiyal2, 1Geology and Mineral Resources Group, CSRE, Indian Institute of Technology, Bombay, ([email protected]); 2Birbal Sahni Institute of Palaeosciences, Lucknow, Uttar Pradesh 226007 ([email protected]).

Introduction: This study aims at constraining the Channels originating from tributary canyons: origin of recent channels within the wallslopes of Ju- Three channels (one on the South-East, and two on the ventae Chasma based on morphological and analogous North-West wall) originate from tributary canyons. The evidences. Juventae Chasma is a box canyon oriented channel on the South-East wall is deeper and has an oblique to the main WNW-ESE trend of the Valles inner channel. The other two channels on the North- Marineris canyons system. Channels are observed in West wall are not easily recognizable because of low eastern, southern and western slope of the Chasma wall topographic contrast between channel floor and walls. [1] which may have different formational histories Moreover it appears that some parts of the channels are (Fig.1). buried under chaos blocks. Dateset: This study is based on data collected by Analogues site: We compare the Martian fluvial Context Camera (CTX) [2] and High Resolution Imag- features to channels in Ladakh which are formed by ing Science Experiment (HiRISE) [3] from Mars Re- melting of valley glacier. Ladakh is a high altitude connaissance Orbiter (MRO) and High/Super Resolu- (3500m-5500m above sea level) cold and dry desert tion Stereo Color Imager (HRSC) [4, 5] on-board Mars with salt lakes, low annual precipitation (102 mm), Express. high diurnal and annual temperature variations (ranging Observations: In a previous paper we describe flu- from -30° to 30° Celsius) and high UV influx [8]. Fig- vial channels from the walls of Juventae Chasma and ure 4 shows field image of a stream emerging through grouped them into four classes based on their morphol- multiple alcoves fed by seasonally melt ice in Nubra ogy [1]. Following is the location-wise detailed de- valley (34˚31’43’’N 77˚31’97”E). Such type of chan- scription of channels with some more observations: nels are also commonly associated with debris flows. East Wall: A single channel about 42 km in length Discussion: The channels on the East and West and > 1.5 km width emanates from an alcove and with walls appear similar to the Hesperian and Amazonian- occasional first order streams joining it (Fig.2). This aged valleys which occur in equatorial [9] and midlati- channel occurs within a collapse pit inside a crater. tude regions [10, 11, and 12]. Age determination using South Wall: The source region for the channels in crater count agree to the same [1]. In contrast, the most cases are alcoves in the chasma walls. The aver- channels on the South wall appear old and degraded. In age length and width of these channels are ~3-4 km and addition, the offsetting of these South wall channels by ~500 m, respectively. A majority are first order chan- a wall-parallel fault suggests that their formation took nels and show degraded morphology (Fig.1). A normal place at a time when chasm-forming tectonism was still fault, striking parallel to the chasm south wall offsets active. Inverted channels on the West wall are also these channels. relatively degraded and superposed by other channel West wall: Here we observe a dendritic network of networks. These seem to represent a dense network of channels, superposing an older generation of narrow older channels. The channels emanating from the tribu- inverted streams. Stream orders reach upto four. Ex- tary canyons, particularly on the North-West wall are cept for one, none of the channels has a clear source also old in appearance and are possibly superposed by region, these channels begin abruptly as shown in Fig. chaos blocks. If this is true, they might also be quite 3. old. Inverted channels: Older generation of narrow in- The higher stream order of the channels on the West verted streams (2-3 km long, ~100m wide) without wall, and apparent absence of a source region (such as well-defined source region are present on the West an alcove) could suggest these channels were precipita- wall (Fig.3). These have been cut by younger dendritic tion fed. The channel on the East wall, originates from channels. The infilling material appears to be the light an alcove on the inner wall of a collapse pit within a toned mound forming material. Some of these channels crater. The straight channel segments, associated al- appear to be present on the top surface of a detached coves, and tributaries which have a similar origin favor block of chasm wall. Stream orders of three are ob- their formation from the melting of snow accumulated served in these channels. A second group of inverted in the alcoves. However the long stream length suggest channels of length 1-2 km and width ~150 m are pre- that there was a continuous supply of voluminous water sent on the South wall. We observe that stream width which could be supplied by a stable ice body (such as a increases upon merging of tributaries. glacier), and not mere seasonal snow accumulation. Lunar and Planetary Science XLVIII (2017) 2603.pdf

The South wall channels are mostly unbranched, and originate from chasm wall alcoves. These features fa- vor their formation from water generated by melting of snow which accumulated in the alcoves. Whether this Fig 2 snow was glacial, seasonal, or ground-ice is a matter for further research. Channels emanating from amphi- theater headed tributary canyons, are possibly caused by groundwater sapping, the source of which could be a shallow confined aquifer or deep cryovolcanism [13]. Fig 3 The inverted channels are an older generation of streams which were filled in with light toned materials (especially the ones on the West wall) and later these materials were lithified to become resistant, positive relief forming features. The high stream order indicate their formation from atmospheric precipitation of liq- uid water. We find the morphology and setting of the channels on the East and South walls match our observation in Ladakh, which is fed by an ice source occurring within an alcove/cirque. Further study is required to distin- guish channels fed by glaciers from those fed by sea- sonal snow/frost. The frequent association of debris flows [14] with these channels is again supportive of Fig.1. CTX mosaic of Juventae Chasma showing location of channels this view. The debris flows could suggest episodic and inverted channels (IC). flooding caused due to snowpack melting. Overall, Juventae Chasma presents a variety of drainage networks of different ages. This clearly indi- Fig.2. Individual cates that liquid water flow was a common phenome- channels on East wall non in this region of Mars, and it could have extended emerging from the (may be episodically, if not continuously) post opening crater collapse pit. Few of the chasma to the Late Amazonian. minor streams are References: [1] Singh et al. (2016) Lunar Planet. Sci. joining the main XLIV Abstract#1766. [2] Malin et al. (2007) JGR: Planets, channels (image 112.E5. [3] McEwen et al. (2007) JGR: Planets, 112.E5 [4] source:CTX mosaic of Neukum (2004) Nature, 432.7020: 971-979. [5] Jaumann et al. Google Mars). (2007) Planetary and Space Science, 55.7 (2007): 928-952. [6] Mangold et al. (2008) JGR: Planets, 113.E8 [7] Weitz et al. (2010) Icarus, 205.1: 73-102 [8] https://en.climate- data.org/location/24802/ [9] Palucis et al. (2014) JGR: Planets, 119.4, 705-728. [10] Dickson et al. (2009) GRL, 36.8. [11] Fig.3. CTX Howard and Moore (2011) JGR: Planets, 116.E5. [12] Hobley mosaic images et al. (2014), JGR: Planets 119.1, 128-153. [12] Wilson et al. showing den- (2016) JGR: Planets, 121.9, 1667-1694. [13] Mara et al (2015). dritic channels Earth Surface Dynamics 3.3 (2015): 389-408. [14] Sarkar et al. of the West wall (2016), Lunar Planet. Sci XLVI Abstract#1876 cutting across

the older invert- Fig. 4. Chan- ed channels. nels in Nubra Valley, Ladakh formed by seasonal ice melt.