Morphology and dynamics of inflated subaqueous basaltic lava flows

Abstract

During eruptions onto low slopes, basaltic Pahoehoe lava can form thin lobes that progressively coalesce and inflate to many times their original thickness, due to a steady injection of magma beneath brittle and viscoelastic layers of cooled lava that develop sufficient strength to retain the flow. Inflated lava flows forming tumuli and pressure ridges have been reported in different kinds of environments, such as at contemporary subaerial Hawaiian-type volcanoes in Hawaii, La R eunion and Iceland, in continental environments (states of Oregon, Idaho, Washington), and in the deep sea at Juan de Fuca Ridge, the Galapagos spreading center, and at the East Pacific Rise (this study). These lava have all undergone inflation processes, yet they display highly contrasting morphologies that correlate with their depositional environment, the most striking difference being the presence of water. Lava that have inflated in subaerial environments display inflation structures with morphologies that significantly differ from subaqueous lava emplaced in the deep sea, lakes, and rivers. Their height is 2-3 times smaller and their length being 10-15 times shorter. Based on heat diffusion equation, we demonstrate that more efficient cooling of a lava flow in water leads to the rapid development of thicker (by 25%) cooled layer at the flow surface, which has greater yield strength to counteract its internal hydrostatic pressure than in subaerial environments, thus limiting lava breakouts to form new lobes, hence promoting inflation. Buoyancy also increases the ability of a lava to inflate by 60%. Together, these differences can account for the observed variations in the thickness and extent of subaerial and subaqueous inflated lava flows.

Three‐Dimensional Seismic Imaging of Ancient Submarine Lava Flows: An Example From the Southern Australian Margin

“…The dendritic flows also contain pathways that are fed from plateaus. The plateaus have similar dimensions and morphologies to the inflation plateaus imaged by Deschamps et al () and Mitchell et al (), supporting our interpretation that the plateaus represent features related to lava emplacement. Additionally, the plateaus described by Mitchell et al () feed dendritic, smaller‐scale lobes which are interpreted to form as a result of breakout and inflation, similar to subaerial pāhoehoe.…”

Ovda Fluctus, the Festoon Lava Flow on Ovda Regio, Venus: Not Silica‐Rich

“…The area and volume of Ovda Fluctus are significantly larger than those of terrestrial dacitic or rhyolitic lavas, but well within the ranges of terrestrial basalt flows ( Table 2). The central depressed area of Ovda Fluctus has few (if any) counterparts among silica-rich lava constructs, which typically have flat tops or central domes (Fink & Griffiths, 1998); however, depressed centers do occur on thick basaltic lava flows, where they are generally inferred to form by drain-back or breakout of the molten lava (Deschamps et al, 2014;Stovall et al, 2009;Swanson & Peterson, 1972;Watanabe et al, 1998).…”

Segmentation and eruptive activity along the East Pacific Rise at 16°N, in relation with the nearby Mathematician hotspot

“…Inflated lava flows have been described by Deschamps et al [2014]. They form prominent flows, forming horizontal plateaus up to 700 m in diameter, with a flat or slightly depressed summit.…”

“…These flows are made up of sheet and ropy lavas. They arise from the inflation of the Pahoehoe-type lava lobes emplaced on nearly flat seafloor [Deschamps et al, 2014].…”