Laboratory Simulations of Submarine Lava Flow Morphology: A Quarter Century of Progress

Abstract:

Mid-ocean ridge (MOR) lava flows are among the most common landforms on Earth, yet only recently have they begun to be observed scientifically while active. Thus most of our knowledge of their emplacement is inferred from their appearance. A widely-used tool to decipher these processes is laboratory simulation of flow morphology using polyethylene glycol (PEG) wax. In contrast to subaerial eruptions, which vary widely in magma composition and atmospheric temperature and pressure, MOR lavas form under relatively uniform conditions, making application of laboratory simulations more straightforward than for subaerial cases.

Since 1989, we have conducted thousands of experiments using PEG emplaced in cold water, because the wax forms a solidifying crust that influences morphology in a similar way to natural basaltic lavas. We have varied eruption rate, wax and ambient temperatures, wax composition, underlying slope and roughness, vent geometry, and eruption episodicity. Our most significant early conclusion was that nearly all commonly-observed lava morphologies, on land and undersea (e.g., levees, folds, rifts, pillows), can be reproduced by varying the relative rates at which surface crust forms and flows advance. For subaerial flows, crust growth rate depends mainly on lava rheology (mostly composition) and eruption rate. Because the chemistry of MOR lavas is relatively uniform, the most common submarine morphologies (pillows, sheets, jumbled, striated, etc.) can be directly correlated with eruption rate, as long as underlying slope is known. This offered the first and still most widely-used method for estimating emplacement rates of submarine volcanic terranes.

Application of this approach began when submarine eruptions were first being acoustically detected. Eruption rates could only be estimated at a few sites, and interpretive measurements were painstakingly slow. Still, observed structural and morphological differences between fast and slow spreading ridges could begin to be quantified. Now, with new digital image analysis techniques and an explosion of undersea monitoring, including at sites of active vents, large swaths can be characterized. These advances suggest it may be time to revisit earlier lab experiments and refine the classification of submarine lava and ridge characteristics.