SHAPES OF MUD VOLCANOES: GEOMORPHIC SIMILARITIES, DIFFERENCES AND IMPLICATIONS FOR MARS. D. Oppo1, M.A. Chan2, C. Berry3, G. Komatsu4, 1School of Geosciences, Universi-ty of Louisiana at Lafayette (611 McKinley Street, Lafayette, LA 70503, USA, davide.oppo@louisiana.edu), 2Dept. of Geology & Geophysics, University of Utah (115 S. 1460 E. Rm 383 FASB, Salt Lake City, UT 84112-0102, USA, marjorie.chan@utah.edu), 3Dept. of Mathematics University of Louisiana at Lafayette, 4International Research School of Planetary Sciences, Università d'Annunzio (Viale Pindaro 42, 65127 Pescara, Italy).

Introduction: Mud volcanoes have long been rec-

ognized as important windows into the deep subsur-face. Their deposits have a high potential in providing and preserving biosignatures and information on the deep geology in contexts where these information would otherwise be non-retrievable. The hypothesis of mud volcanism on Mars has been advanced to explain the origin of numerous mound features observed in various regions of the planet, such as Utopia Planitia [1], Acidalia Planitia [2], Isidis Planitia [3], Chryse Planitia [4]. Yet, the exact nature of these features has not been proved decisively. Simple morphometric analyses, such as height/width ratio, show similarities between terrestrial and Mars mud volcanoes, but unre-lated geologic processes may result in comparable landforms (e.g. cinder cones) [5,6].

Mud volcanoes are widespread across the Earth’s surface and their diverse morphology reflects the vari-ous settings controlling eruption and erosion processes. However, grain size is inherent in the name mud volca-noes, and it is likely that a broader range of grain sizes and corresponding features (e.g., sand injectities; [7,8]) should also be considered. Surprisingly, a comprehen-sive characterization of process-related geomorphology of terrestrial mud volcanoes is still lacking, thus un-dermining our ability to effectively recognize these structures by remote sensing. A dataset of mud volca-noes characteristics and measurements can provide insight into the evaluation of mud volcanism in our solar system.

Methods: We compiled a dataset of 244 repre-sentative active and fossil terrestrial on-land mud vol-canoes occurring in N. America, Europe, Middle East, and Asia. Morphometric parameters and features de-scriptions (e.g., gryphons, calderas, visible mud flows) were derived from Google Earth satellite images. With the resolution of this imagery, there may be ~ up to 10% error in measurements and selection of feature boundaries. Additionally, elements less than 0.5 m in diameters cannot be easily recognized.

Results: The studied mud volcanoes include all representative morphologies: cones (57% of total), gryphon clusters (18%), mud pies (17%), and flat/negative features (9%). The majority of investigat-ed mud volcanoes are active (88%) and are represented in all the morphological groups. Fossil examples (12%)

are commonly conical and are more challenging to identify [8-9].

Gryphons are common morphologies defined as small-scale (<3-4 m high), steep conical emission vents [10]. They frequently occur either on the flanks or on the summit of mud volcanoes but, when in clusters of 10 or more, gryphons can form independent emission areas displaying a distinctive surface geomorphology (Fig. 1). Mainly, mud volcano morphologies have a relatively low number of detectable emission vents (<10) (Fig. 2). However, mud pies, caldera clusters, and salse groups (seepage lakes reaching several me-ters in diameter and depth, [10]) show a bimodal dis-tribution with up to ca. 50 vents.

The calculated H/W ratios of terrestrial mud volca-noes (excluding crater lakes for which H/W is zero) ranges between 0.0003 and 0.3333 (mean 0.037, medi-an 0.022). The H/W ratio of hypothesized Mars mud volcanoes ranges between 0.005 and 0.127 (mean 0.043) [5], thus fitting in the H/W range observed on Earth for both mud volcanoes and other features [5].

Fig. 1: Terrestrial association of mud pie and gryphons clus-ter morphologies (Azerbaijan, 40.318N, 49.307E). Discussion: Despite Mars mounds may show morphol-ogies comparable to Earth mud volcanoes (Fig. 3), their variety can lead to challenges in interpreting their origin. The H/W ratio, commonly employed to relate the general morphometry of mud volcanoes on Earth and Mars, is ineffective in providing significant infor-mation because of the similarity among an extensive group of geological morphologies. Thus, successful identification of mud volcanoes requires the integration of a wider array of morphological observations in mud volcanoes. Terrestrial mud volcanoes show diverse morphological elements that are frequently spatially associated (Fig. 1). The recognition of these unique

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ensembles has the potential of advance our ability to identify mud volcanoes by remote sensing. For exam-ple, terrestrial mud volcanoes are frequently associated with gryphons (Fig. 2), so that their distribution and number can help distinguish the occurrence of subsur-face structures and fluid dynamics. Furthermore, the particular conditions regarding Mars gravity and at-mosphere may need to be taken into account. For ex-ample, a laboratory study simulating mud eruption un-der the low pressure environmental conditions has yielded observation of boiling water influencing the mud behavior [11].

An important aspect to consider is the preservation of mud volcano features after the end of the main emis-sion activity. Fossil mud volcanoes pose a challenge in their recognition by remote sensing because their dis-tinctive morphologies are progressively obscured by erosional processes, particularly on Earth where liquid water plays a significant role in the processes. The ma-jority of fossil mud volcanoes on Earth do not show remnants of a summit vent or mud flow, which means preservation depends on characteristics such as relief, extent, and mud or sediment density. Additionally, because of the variability of emission intensity and mud properties, some well-developed mud volcanoes do not show morphologically evident mud flows even during active periods.

Conclusions and Future work: Mud volcanoes may represent exceptional windows in the Mars subsur-face, with great potential to provide information on the subsurface geology, crustal fluid dynamics, and poten-tial biological signatures. Because the successful iden-tification of Martian mud volcanoes depends on the ability to recognize distinctive morphologies by orbital data, we must first fully characterize the terrestrial ana-logs. Our future work will include developing a sys-tematic morphological and morphometric study of mud volcanoes on Earth for an in-depth evaluation and comparison to the Martian examples.

References: [1] Skinner J. A. and Tanaka K. L. (2007) Icarus, 186, 41–59. [2] Oehler D. Z. and Allen C. C. (2010) Icarus, 208, 636–657. [3] Davis, P. A. and Tanaka, K. L. (1995) LPS XXVI, 321-322. [4] Komatsu G. et al. (2016) Icarus, 268, 56–75. [5] Hemmi R. and Miyamoto H. (2019) 50th LPS, Abstract # 2132. [6] de Pablo M. and Komatsu G. (2009) Ica-rus, 199, 49–74. [7] Wheatley D. F. et al. (2019) Ica-rus, 328, 141-151. [8] Oppo D. and Capozzi R. (2016) Basin Res., 28, 827–839. [9] Omrani H. and Raghimi M. (2018) Mar. Pet. Geol., 96, 615–626. [10] Mazzini A. and Etiope G. (2017) Earth-Science Reviews, 168, 81–112. [11] Brož P. et al. (2019) LPS 50th, Abstract #1769.

Fig. 2: Terrestrial occurrence of gryphons and number of emission vents for each mud volcano morphology (Tot. vents n.=2026).

Fig. 3: a) Candidate Mars mud volcano in Acidalia Mensa and b) analog on Earth (Azerbaijan). The two structures show a similar set of features which combined occurrence can help to confirm the nature of the Martian example.

1041.pdf51st Lunar and Planetary Science Conference (2020)