Statistical distribution of tumuli on pahoehoe flow surfaces: Analysis of examples in Hawaii and Iceland and potential applications to lava flows on Mars

Spatial distributions of tumuli on lava flow surfaces can be quantitatively linked to subsurface inflation processes. Three distinct styles of flow emplacement are studied: (1) lava flows undergo inflation that changes as a function of space and time resulting in random spatial distributions of tumuli, (2) lava flows with preferred pathways result in systematic clustering of inflation features, and (3) established tubes or narrow pahoehoe flows produce chains of tumuli. Statistical analyses are required to distinguish between styles one and two. Comparison of the spatial distribution of tumuli on a portion of a lava flow at Mauna Ulu with the Poisson distribution indicates that tumuli are randomly distributed on the flow surface, typical of style one emplacement where small‐scale topographic variability and low slope influence development of preferred pathways that evolve over time. At Thrainsskjoldur, direct statistical comparisons to the Poisson spatial distribution are inconclusive but nearest‐neighbor analysis indicates significant clustering. An initially random spatial distribution is inferred that developed preferred pathways and systematic clustering of inflation features, as with style two. At Elysium Planitia on Mars, the flow margin is significantly deficient in inflation features, while away from the margin, the flow exhibits a random spatial distribution of tumuli typical of style one emplacement. The flow is interpreted as multiple units or a single flow that migrated in space during emplacement. At the 1843 flow on Mauna Loa, tumuli occur on a linear trend, consistent with style three emplacement.