IDENTIFICATION AND ANALYSIS OF ROOTLESS VOLCANIC CONES ON MARS

Transcription

1 IDENTIFICATION AND ANALYSIS OF ROOTLESS VOLCANIC CONES ON MARS Nicole R. VanDeBerg Department of Geology and Geophysics University of Hawai i at Mānoa Honolulu, HI ABSTRACT Rootless cones are features on the Martian surface resulting from the explosive interaction of lava and water or ice in the underlying substrate. These geologic features are visually definable by circular cones, craters, vertical relief, and grouping in fields. The mapping of these features is important to NASA and the scientific community for a number of reasons including a better understanding of: the evolution of volatiles of Mars, previous and current Martian climate, igneous processes, locations on Mars favorable to biotic development, and areas possibly containing resources to be used for future human and robotic exploration. The course of this project processed images from on-line image galleries derived from NASA Mars Project missions. The processing of these images included using Adobe Photoshop to mark candidate rootless cones, ambiguous cone features, and the centers of both sets of features in MOC, Themis, and HiRise images. This data can then be used in hydrology modeling and other pertinent studies. INTRODUCTION- BACKGROUND AND PURPOSE Rootless cones, not to be confused with primary cones formed over volcanic conduits, are formed on top of lava flows (Fig. 1). Their formation is the result of lava interaction with water or ice in the substrate. As a lava flow moves over the water bearing substrate, steam is produced, causing an explosive reaction. As the reaction occurs, scoria and tephra build up around the explosion sight. This build-up of debris forms a cone (Fig. 2) [Fagents et al., 2002]. When an explosion stops at one site, explosivity at another site may ensue. The halting of activity at a site can result from exhausted water or lava supply at that site. This pattern of resource exhaustion results in the formation of cone fields (Fig. 3) [Bruno et al., 2004; Bruno et al., 2006]. These fields can consist of hundreds of cones with the features ranging from tens to hundreds of kilometers in diameter and heights of kilometers [Bruno et al., 2006]. Rootless cones are key to our understanding of the Martian surface. The studying of these features can lead to a better understanding of: the evolution of volatiles of Mars, previous and current Martian climate, surface evolution, and igneous processes on the planet. Because the presence of water in liquid or solid form is essential to their development, rootless cones act as a probe to determine the location and relative time periods of H 2 O in liquid or solid form in and on the Martian surface. The mapping of these features is significant to the research of biotic development, as the combination of water and volcanic heat at these sites could provide essential precursory conditions. The mapping of these features can also be used as a tool to determine if there are water or ice deposits on the planet which could be utilized as resources in human and robotic exploration [Fagents et al., 2002]. 74

2 Figure 1. Martian lava flow containing rootless cone fields Figure 2. Rootless volcanic cones in the Cerberus region of Mars. MOC image S , 1.7 m/pxl. 75

3 Figure 3. Formation of a rootless cone field Through the studying of these features, not only can the location and approximate time period of water in the substrate be determined, but possibly the hydraulic conductivity of the substrate and therefore, the amount of water at the location. This can be done using hydrology modeling. This project involved locating and marking hundreds of individual rootless cones within a field. This data can then be taken and, assuming the location of each rootless cone as an analogue to an extraction well, be used according to the concept of unconfined aquifers and equations associated with them as detailed in Flows in Porous Media by Turcotte and Schubert along with hydrology modeling software to solve for the hydraulic conductivity. Because the studying of the location of each specific cone within a field is highly important to solving for the hydraulic conductivity, it was my goal to analyze satellite images of rootless cone fields and mark the location of each individual cone. This was done by determining visual criteria of rootless cones and using Adobe Photoshop to mark these locations. A one pixel mark in the center of each marked location helps to further narrow the location of the feature and can also be used to run statistical analysis such as skewness and kurtosis (Fig. 4), processes that can serve as a verification that the features I have marked are, in fact rootless cones.[bruno et al., 2006] 76

4 on Mars Figure 4. Skewness and kurtosis of nearest neighbor results [Bruno et al., 2006] METHODS This study of rootless cones was done via satellite imagery. These sources included: Mars Orbital Camera (MOC) narrow-angle, with a resolution of three meters per pixel; Thermal Imaging Emission System (THEMIS) visible images, with a resolution of 100 meters per pixel; and High Resolution Imaging Science Experiment (HiRise), with a resolution of 0.3 meters per pixel. These images allow the viewer to readily distinguish features meters, meters, and meters in diameter respectively. These data are available online for searching and downloading at the following URL s: Mars Orbital Camera (MOC) on The Mars Global Surveyor: and Thermal Emission Imaging System (THEMIS) on Mars Odyssey: High Resolution Imaging Science Experiment (HiRise) on the Mars Reconnaissance Orbiter: There are specific characteristics that distinguish rootless cones form other geologic features on the Martian surface. There are also numerous processes that can distort the shape of rootless cones. As I processed the images, I set criteria as to what characteristics features were to have to be marked as rootless cones. The original criteria for marking these features was based both on criteria written in previous papers such as those noted at the end of this report. Such papers name rootless cones as coned, cratered features with a distinct vertical relief occurring in groups. These groups can be linear, circular, or seemingly undefined clusters. I expanded upon these criteria, only choosing features that were distinct. Due to the layering and weathering of these features, there are features that may be rootless cones, but do not distinctly meet these visual criteria. It can be determined if these features are rootless cones by running the afore mentioned statistical 77

5 nearest neighbor analysis of skewness and kurtosis on a one pixel marking of the center of the features. To mark the rootless cones, ambiguous cones, and one pixel white dot center, I used Adobe Photoshop. I made multiple layers in the program. These layers consisted of the original image (Fig. 5) taken near 25.5 degrees latitude and degrees longitude depending upon image source, the rootless cone markings, the ambiguous cone markings, and the one pixel crater center marking. I arbitrarily chose a shade of fuchsia to designate the visually identified rootless cones (Fig. 6) and turquoise to designate the ambiguous cones (Fig. 7). The marking designation consisted of circles sized comparatively to the feature size on the computer screen. Figure 5. Crop of an original HiRise image to be processed 78

6 Figure 6. Crop of same (Fig. 5) HiRise image with identified rootless cones marked Figure 7. Crop of above (Fig. 6) HiRise image with ambiguous Cones also marked. 79

7 RESULTS/ DISCUSSION This project resulted in three processed images. These images included one image each from the Themis, MOC, and, HiRise galleries all from similar locations respective to pixel size. These images will then be used in the afore mentioned hydrology modeling. In the process of creating these images, I also established visual criteria. To be marked as a rootless cone, the geologic feature must be visually coned, cratered, have a higher vertical relief than comparative features such as an impact crater. The feature must also occur in a group or field. There are many features that I suspected to be possible rootless cones, but were ambiguous. These features could have become distorted due to a number of reasons including subsequent lava flows, coalescence of the features, and weathering. These features were marked as ambiguous cones. There were also features that seemed to fit the criteria of rootless cones; however, they were not near any other features and therefore are most likely not rootless cones. The initial criteria I had set based on papers and discussions with Dr. Sarah Fagents proved to be very accurate when I began looking at the images. The cones looked as I had expected and were grouped as I had anticipated both criteria which I have previously discussed in this paper. I was not anticipating the large number of ambiguous features, and had to adjust my criteria as previously mentioned to accommodate these features. CONCLUSION In conclusion, rootless cones are geologic features on the Martian surface formed by the interaction between lava and ground-water or ice. These features are circular, coned, cratered, tend to have a higher vertical relief than other cratered features on Mars (such as impact craters), and form in groups over a lava flow. The visual identification of these features can be obscured due to weathering, subsequent lava flows, or coalescence of the features. The researching of these features can give insight into the climate history of Mars, the Martian water cycle, areas of possible biotic development, and areas of possible resources. These features can be studied visually, using satellite imagery, and mathematically, using statistical analysis. The location of individual rootless cones within a field can be used in hydrology modeling to determine the hydraulic conductivity of the substrate, and therefore the amount of water used in a reaction at a specific site. This study found the location of these individual features within specific lava flows using HiRise, MOC, and Themis images in Adobe Photoshop. This was done using Photoshop layers, marking the identified rootless cones in fuchsia, the ambiguous rootless cones in turquoise, and the one pixel mark of the centers in white. This data can then be used in hydrology modeling and other pertinent studies. ACKNOWLEDGEMENTS I would like to thank: NASA and the Hawaii Space Grant Consortium for providing me with the amazing opportunity to assist in research in the field of Geophysics, Dr. Jeffrey Gillis- Davis for encouraging me to pursue a NASA Space Grant, Christopher Hamilton for his inspiration and reminders to retain a sense of awe toward the universe; and Dr. Sarah Fagents for her mentoring, smile, and encouragement. I would also like to thank my mother, Kathy VanDeBerg; grandparents, Myron and Babe Olson; and friend, Joshua Hampton; your pride in me is fuel for success. 80

8 REFERENCES Bruno B. C., Fagents S. A., Hamilton C. W., Burr D. M., Baloga S. M. (2006) Identification of volcanic rootless cones, ice mounds, and impact craters on Earth and Mars: Using spatial distribution as a remote sensing tool. J. Geophys. RES., 111, E06017, doi: /2005je Bruno B. C., Fagents S. A., Thordarson T., Baloga S. M., Pilger E. (2004) Clustering within rootless cone groups on Iceland and Mars: Effect of nonrandom processes. J. Geophys. Res., 109, E07009, doi: /2004je Fagents S. A., Lanagan P., Greeley R. (2002) Rootless cones on Mars: a consequence of laveground ice interaction. Volcano-Ice Interaction in Earth and Mars. Geological Society, London, Special Publications, 202, Turcotte D. L., Schubert G. (2002) Flows in porous media. Geodynamics, Ch. 9 81