Morphometry and Cluster Analysis of Low Shield Volcanoes on Earth and Mars

Abstract:

Volcanoes are common on all terrestrial planets and their morphology is influenced by eruption mechanisms, volumes, and compositions and temperatures of the magmas; these are in turn influenced by the tectonic setting. In an attempt to better understand the relationship between morphometry and volcanic processes, we compared low-shield volcanoes on Syria Planum, Mars, with basaltic shields of the eastern Snake River Plain (eSRP).We used 133 volcanoes on Syria Planum that are covered by MOLA and HRSC elevation data and 246 eSRP shields covered by the NED. Shields on Syria Planum average 191 +/- 88 m tall, 12 +/- 6 km in diameter, 16 +/- 28 km³ in volume, and have 1.7° +/- 0.8 flank slopes. eSRP shields average 83 +/- 44 m tall, 4 +/- 3 km in diameter, 0.8 +/- 2 km³ in volume, and have 2.5° +/- 1 flank slopes.

Bivariate plots of morphometric characteristics show that Syria Planum and eSRP low shields form the extremes of the same morphospace shared with some Icelandic olivine tholeiite shields, but is generally distinct from other terrestrial volcanoes. Cluster analysis of SP and eSRP shields with other terrestrial volcanoes separates these volcanoes into one cluster and the majority of them into the same sub-cluster that is distinct from other terrestrial volcanoes. Principal component and cluster analysis of Syria Planum and eSRP shields using height, area, volume, slope, and eccentricity shows that Syria Planum and eSRP low-shields are similar in shape (slope and eccentricity). Apparently, these low shields formed by similar processes involving Hawaiian-type eruptions of low viscosity (mafic) lavas with fissure controlled eruptions, narrowing to central vents. Initially high eruption rates and long, tube-fed lava flows shifted to the development of small lava lakes that repeatedly overflowed, and on some with late fountaining to form steeper spatter ramparts. However, Syria Planum shields are systematically larger than those on the eastern Snake River Plain. The larger size of Syria Planum shields is likely due to the smaller gravity of Mars, requiring larger magma batches to generate sufficient buoyant force to overcome the strength of rocks in the lithosphere and rise to the surface. Thus, Syria Planum lavas erupt at and higher rates generating larger volcanoes with slightly smaller slopes.