Origins of Sinuous and Braided Channels on Ascraeus Mons, Mars
What: Water has clearly played an important part in the geological evolution of Mars. There are many features on Mars that were almost certainly formed by fluvial processes – for example, the channels Kasei Valles and Ares Vallis in the Chryse Planitia area of Mars are almost certainly fluvial features. On the other hand, there are many channel features that are much more difficult to interpret – and have been variously attributed to volcanic and fluvial processes (Bleacher et al., 2008; Murray et al., 2009). Clearly unraveling the details of the role of water on Mars is extremely important, especially in the context of the search of extinct or extant life on Mars. In this project we will build on recent work that we have done in determining the origin of some channels exposed in the southwest rift apron of Ascraeus Mons in the Tharsis region of Mars (Fig. 1). We plan to take advantage of the recently available datasets to map and analyze similar features on Ascraeus Mons and perhaps to expand this analysis to other areas of Mars. A clearer understanding of how these particular channel features formed might lead to the development of better criteria to distinguish how other Martian channel features formed. Ultimately this might provide us with a better understanding of the role of volcanic and fluvial processes in the geological evolution of Mars.
When: July 6-August 3
- Week 1: Introduction to Mars, Introduction to Mars missions and available datasets, Introduction to GIS, Project background, development of individual projects. Project database development – downloading and assembling the necessary datasets. Most of this will be done at F&M in the GIS computer lab. We plan to spend one day at GSFC where we will hear from NASA researchers about Mars research and tour the labs.
- Week 2: Mapping and analysis of the channel features.
- Week 3: Interpretation and expansion of the research. Field trip to Hawaii (details to be determined).
- Week 4: Completion of Part 1 of the research. Development of the academic year follow-on projects. Data collection, formulation of goals. We anticipate that the students will be able to present the results of their summer work to interested scientists at GSFC towards the end of this week.
Where: Franklin & Marshall College, Lancaster Pa; NASA Goddard Space Flight Center, Greenbelt Md (day trips); Hawai’i (5 day trip).
Who: 4 students and Andrew de Wet (F&M), Jake Bleacher (NASA-GSFC), Brent Garry (Smithsonian)
Project Overview and Goals
The observations of sinuous channels on the Moon and Mars has led to debates over their formation either as a result of fluvial or volcanic processes. Apollo samples showed that fluvial processes did not form channels on the Moon (Heiken et al., 1991). However, the acquisition of new Martian data has heightened the debate over the origin of some sinuous channels. This debate demonstrates the similar characteristics of fluvial and volcanic channels and their products (Leverington, 2004). Recently we presented evidence that suggests that at least one channel system on Ascraeus Mons, previously interpreted to have formed by fluvial processes (Murray et al., 2010), was likely formed by flowing lava (Bleacher et al., 2010) (Fig. 2). In this study we compared the morphology of this braided and sinuous channel on the south-west rift apron of Ascraeus Mons to similar features on the 1859 Mauna Loa lava flow, Hawai’i and features within Mare Imbrium on the Moon. We showed that while the proximal and medial parts of this channel showed features that are analogous to fluvial channels, these parts also share similarities with volcanic features. Our analysis showed that the distal section of the channel was clearly volcanic, which strongly suggested that the entire feature was volcanic in origin. The Keck project will expand on this study by examining other channels on Ascraeus and perhaps in other locations on Mars.
Background and previous work
The development of the Tharsis Montes includes main flank formation followed by rift zone activity (Crumpler & Aubele, 1978) but the relationship between the two is not entirely clear. It is suggested that these two episodes represent a magmatic continuum (Wilson et al., 2001), two temporally unique but spatially overlapping magmatic events (Bleacher et al., 2008), and a magmatic event (main flanks) followed by hydrothermal and fluvial activity (rift aprons) (Murray et al., 2009).
In order to try to understand whether volcanic and/or fluvial processes contributed to the evolution of Tharsis Montes, our recent study focused on a channel exposed on the east side of the southwest apron of Ascreaus Mons (Fig. 1). Earlier studies done by us (Bleacher et al., 2008; Trumble et al., 2008) and by other researchers (Murray et al., 2009; Mouginis-Mark and Christensen, 2005) had suggested that the channel resulted from fluvial erosion. These studies were hampered by the limited data available at the time which meant that only part of the feature (its proximal region) could be studied. Sufficient data is now available, enabling comprehensive studies of these features in their entirety. We used a combination of MOLA (gridded data product), THEMIS, HRSC, and CTX data to examine the channel. The study also included field work on the 1859 Mauna Loa lava flow, Hawai’i, using a Trimble R8 Differential GPS with vertical and horizontal accuracies of 2-4 and 1-2 cm respectively. We compared this feature with Apollo metric images of Mare Imbrium. The lunar and terrestrial comparisons were used to provide insights into the formation of the Martian channel. The results of this study were presented at LPSC in March, 2010 (Bleacher et al., 2010). Additionally, Bleacher and Garry recently returned from Hawai’i where another analog, the 1974 Southwest Kilauea rift flow, was also studied, providing new field insights into the potential development of this feature.
The proximal section extends ~60 km from the fissure and displays anabranching, braided and hanging channels, terraced channel walls, no levees, “streamlined” islands, and flow margins that are difficult to detect or are embayed by younger materials. The medial section extends from 60-170 km. Here the channel is composed of one sinuous trench that also lacks clear levees. Generally this section of channel is surrounded by a smooth surface but sometimes shows minor leveed channels leading away from the main channel, probably due to overflow. Flow margins are difficult to determine and are sometimes embayed by younger materials. The distal section extends from 170 to >270 km and displays a significantly different morphology. At 170 km the slope decreases from 0.7-1º towards the fissure to 0.3-0.6º. Here, the channel is located along the axis of a ridge that exceeds 40 m in height. In some locations the channel is roofed over. Furthermore, rootless vents are located along the axis of the ridge. These rootless vents display topographic “caps” up to 1 km in diameter and radiating flows, some extending for several kilometers.
Results of previous work
Visual inspection of the Ascraeus channel’s proximal section shows braided and hanging channels, terraced walls, and streamlined islands all of which have led many to suggest an origin involving fluvial activity based solely upon morphologic inferences. However, new image data have enabled a complete view of the channel, including its distal portions, which display a topographic ridge, well defined flow margins, roofed channel sections, and rootless vents. We suggested that these features are indicative of a volcanic origin for the distal portion of this channel.
The conclusion that the distal portion of this channel is of volcanic origin lead Bleacher et al., (2010) to question the origin of the entire feature. All three sections of the channel show smooth transitions that suggest they are part of one continuous feature. The proximal section displays characteristics suggestive of fluvial activity. As such it is possible that this channel has experienced a mixed fluvial-volcanic history or that proximal volcanic features were mistaken as fluvial. Faced with these two scenarios we examined features of known volcanic origin on the Moon and the Earth for similarities with the Ascraeus proximal section. We observed branching and hanging channels, islands, and terraced channel walls in known volcanic terrains. Together, our observations indicated that the distal section displayed volcanic features and that the proximal section displayed features that could also form in volcanic settings. Additionally we saw no evidence for younger modification of this feature by fluvial processes. Therefore we concluded that this feature was formed by volcanic processes only, followed by partial embayment of its margins by younger materials. This interpreted origin agrees with that for a similar lava channel described on the SW rift apron which also has a rille-like proximal section (Garry et al., 2007).
Although we concluded that the origin of this feature involved volcanic processes, this inference does not preclude the possibility of fluvial activity in this region. It does, however, emphasize the importance of detailed studies of the full extent of individual features and mapping campaigns based on new Martian data.
The primary goal of the Keck project is to extend the study we recently completed to the whole of the southwest rift apron of Ascraeus Mons. We want to know if there are other channels that display similar features to the one we studied and whether these channels can be ascribed to volcanic or fluvial processes. We hope to be able to develop criteria that can be applied to Martian channel features in order to distinguish their mode of formation. Although we have concluded that one specific feature that was previously attributed to fluvial activity, is actually volcanic, it is important that we do not overextend this inference to suggest that all features in the area might share a similar history without conducting the mapping necessary to make such a statement.
Our previous research establishes a baseline from which one or two small student teams can conduct comparable studies of morphologically similar features. Such an approach will establish a data set from which sinuous, anabranching and braided channels can be compared to determine if similar or unique processes have formed this population of features. Determining the presence and role of water in the developmental sequence of the Martian surface is of utmost importance to NASA and the planetary science community.
What are the characteristics and distribution of channels on Ascraeus? What are the characteristics of the proximal, medial and distal parts of these channels?
- What are the similarities and differences between the channels – do all the channels have the same basic morphology? What are the differences? Is there a relationship between the morphology and age of the features?
- What is the origin of the channels – volcanic or fluvial or some combination of both, or another completely different mechanism?
- How do these channels compare to channels on similar volcanoes in the Tharsis area? What about other areas of Mars?
- How do these channels compare to Martian channels that are clearly fluvial in origin?
- Can we develop better criteria to distinguish volcanic from fluvial channels on Mars?
- What do these channels tell us about the geological evolution of Ascraeus? The Tharsis Montes area? Mars generally?
- Did all of these style of features form at one specific period of time in Martian history, or are they stratigraphically and temporally contemporaneous with other eruptions and channel forming events on Ascraeus Mons?
The student projects will comprise two components: Part 1 will be the summer research component, and Part 2, the following academic year component.
Part 1, the summer component will focus on Ascraeus Mons. Each student will be assigned a separate area on the southern flank of Ascraeus. This is the area we know well and it will form the basis on which to expand our research efforts. This component will have the following goals and structure:
- Download, georeference and assemble the required datasets. We will be using a wide variety of datasets including MOLA (gridded data product), THEMIS, HRSC, and CTX data. We will use ArcGIS to build the required databases and compete the mapping and analysis.
- Recognize and develop criteria, and map the various morphological features associated with the channels.
- Measure various parameters such as aerial extent, cross-sections and channel gradients.
- Describe and interpret these morphological features based on our understanding of geological processes on Mars.
- Compare these features to analog features on the earth (including observations made during the 5 day trip to Hawaii) and perhaps the moon.
- Interpret the origin of these features. Develop criteria to distinguish fluvial and volcanic features.
- Place the formation of these features into the broader context of the geological evolution of Mars by mapping their boundaries to determine their relationship with other volcanic (and fluvial) deposits.
- Develop the academic year part of the project.
Part 2, the follow-up academic year component of the project may take one of many forms:
- Complete a similar study in another location in the Ascraeus area – for example the northern apron appears to have similar channels.
- Study similar features on one of the other Martian volcanoes – for example, on one of the other Tharsis Montes volcanoes, or Olympus Mons, or Elysium etc.
- Contrast these channels with Martian channels that are almost certainly formed by flowing water – for example Kasei Valles or Shalbatana Vallis. Examine the similarities and differences between these channel features.
- Do an analog study on the moon or the earth (perhaps expanding on the observations made during the trip to Hawaii).
Broader goals include – exposure to planetary geology, a greater appreciation of the role of NASA in planetary exploration and research, develop experience in doing original research, work together in a team of researchers with a common goal, exposure to research with a broad appeal and relevance.
One of the challenges of doing research on Mars is that everything is based on remote sensing, theoretical considerations, and analog studies. We will take a 5 day trip to Hawai’i to directly observe and measure processes and features that are probably direct analogs to features the students will be mapping on Mars (Figure 3). Jake Bleacher and Brent Garry have done extensive work on several lava flows including the 1859 Mauna Loa lava flow and the 1974 Southwest Kilauea rift flow. These studies have provided new field insights into the processes that may have formed the Ascraeus channel system. Prior to the project next summer, and perhaps in response to observations during the first weeks of the project, we will determine the detailed goals and focus of the field work in Hawai’i.
We might visit the Air and Space Museum in Washington which has an excellent planetary exhibition.
In addition to the Keck Symposium, we will explore the possibility of presenting the results of this research at LPSC in Houston in March 2012.
Recommended Courses (at least two)
- Remote Sensing
- Planetary Geology
Most of the project will be indoors at F&M and GSFC however for the Hawai’i field trip participants need to be able to walk long distances over difficult terrain (lava flows – Figure 4). Students need to bring normal field gear including back packs, sturdy boots, water bottles, rain gear, flashlights etc (details to follow). Accommodation at F&M will be in College housing. Accommodation on Hawai’i has not been finalized and may include camping (details to follow).
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- Bleacher et al., (2010) LPSC, #1612
- Crumpler & Aubele (1978) Icarus, 34.
- Garry et al. (2007) JGRE, doi:10.1029/2006JE002803.
- Heiken et al. (1991) Lunar Sourcebook.
- Leverington, (2004) JGR doi:10.1029/2004JE002311.
- Mouginis-Mark and Christensen (2005) JGRE, doi:10.1029/2005JE002421.
- Murray et al. (2009 in press) EPSL, doi:10.1016/j.epsl.2009.06.020.
- Rowland & Walker (1990) Bull. Vol. 52.
- Schaber (1973) Proc Lunar Sci Conf 4th, 73-92.
- Trumble et al. (2008) LPSC, #1391.
- Wilson et al. (2001) JGRE, doi:10.1029/2001JE001593.