Lava‐Rise Plateaus and Inflation Pits in the McCartys Lava Flow Field, New Mexico: An Analog for Pāhoehoe‐Like Lava Flows on Planetary Surfaces

Abstract

Basaltic lava flows are common on the surface of the Earth and other terrestrial bodies. However, inflation—including a combination of initially rapid molten core thickening and gradual crustal growth—must be accounted for to enable accurate reconstructions of eruption parameters from observed lava flow morphologies. The shape of an inflated lava flow can change significantly over time. Therefore, incorrectly attributing the flow's final thickness to its dimensions in an initially fully molten state will yield excessively high flow rates, erroneous rheological properties, and unreasonably short eruption durations. To develop improved criteria for identifying inflated lava flows, we examined the McCartys lava flow field in New Mexico, USA. This locality provides an example of how pāhoehoe‐like lava lobes can coalesce and coinflate to form interconnected lava‐rise plateaus with internal inflation pits. These structures were examined using a combination of field observations, low‐altitude kite‐based imaging, and quantitative geomorphology using high‐resolution (1.47 cm/pixel) orthomosaics and stereo‐derived digital terrain models. These observations were used to identify characteristics and diagnostics of inflation, thereby facilitating the interpretation of comparable landforms on other planetary surfaces. Lava‐cooling models were also used to estimate the lava emplacement duration of the ~20‐m‐thick flows by demonstrating that the ~8‐m‐thick upper crust exposed within inflation clefts in the southern part of the McCartys lava flow field would have required 1.2–2.5 years of continuous lava supply to form. This places a minimum bound on the total eruption duration, and implies that comparably thick inflated flows on Mars required years to form.

The Lunar Mare Ring‐Moat Dome Structure (RMDS) Age Conundrum: Contemporaneous With Imbrian‐Aged Host Lava Flows or Emplaced in the Copernican?

“…Inflation features in terrestrial basaltic lava flow fields provide clues as to the mode of formation of crater‐like depressions. Some endogenetic surface depressions represent circular lava‐rise (or inflation) pits (Figure 8) formed by the vertical inflation of the host lava flow around local topographic highs on the pre‐flow surface, leaving a depression (e.g., Hamilton et al., 2020; Walker, 1991). In other cases on Earth, lava mounds, all high areas within a lava field, are sometimes locations for the formation of small drained sub‐lava‐crustal lava caves (Grimes, 2002), whatever the process of mound formation.…”

“…The magmatic foam model (Wilson & Head, 2017a, 2018; Wilson et al., 2019) provides an alternative explanation for the absence of fractures associated with RMDSs and their host mare unit, and for the difficulty in discerning impact crater‐like inflation pits (always with highly fractured margins in cases on Earth (Figures 8 and 9; e.g., Garry et al., 2012 and Hamilton et al., 2020). When a flow is emplaced, a more coherent and cooler boundary layer develops at the interface with both space and the cold substrate.…”

Rethinking Lunar Mare Basalt Regolith Formation: New Concepts of Lava Flow Protolith and Evolution of Regolith Thickness and Internal Structure

“…Inflated flows: Surface topography, vesicularity, and mesoporosity-macroporosity: If P4 activity is of long duration, flow inflation of P2 flows can result, elevating and distorting the preexisting solidified flow surface, and introducing several meter-scale topographic irregularities on the recently solidified upper 10.1029/2020GL088334 thermal boundary layer of the flow (Figure 3b). This extremely irregular protolith surface (e.g., Hamilton et al, 2020) will influence the nature of initial stages of regolith development, causing irregular crater formation and ejecta distribution at scales less than the average roughness. The solidified inflated core of the flow at depths of a few meters will consist of a very porous layer of low-density vesicular basalt of significant thickness due to intrusion of very vesicular P3 magma.…”

“…In a high‐flux eruption Phase 4 (somewhat higher than 10 4 m 3 s −1 ), a large fraction of the total dike volume is still available for extrusion as vesicular lava (Figure 2a). This lava is predicted to cause flow inflation (Hamilton et al, 2020; Self et al, 1996), intruding vesicular lava into the still‐hot interiors of the previously emplaced nonvesicular flows. Magma from the shallow parts of the dike (<400 m) feeding such intruding flows would contain water/sulfur compounds that had not yet exsolved.…”

Some Lava Flows May Not Have Been as Thick as They Appear

“…In the other end‐member, wherein the total observed flow thickness is assumed to be only a consequence of lava flow inflation, most models require a relatively continuous, long‐lived effusion rate that gradually thickens the flow lobe (Hamilton et al., 2020; Hon et al., 1994; Kauahikaua et al., 1998; Self et al., 1998). However, if the CFB flow is a fused flow, each constituent flow lobe must inflate to a smaller thickness.…”