Laboratory, field, and numerical approaches to interpreting submarine lava flow morphologies: Where we are, where we want to be, and how to get there

Abstract:

Lava flows emplaced at mid-ocean ridges (MORs) are the fundamental building blocks of oceanic crust, but an active flow at a typical MOR has not yet been observed. Therefore, eruption and emplacement conditions must be inferred from the solidified volcanic morphology, geochemistry and petrology. Using these datasets, combined with laboratory simulations and numerical modeling, reasonable estimates of emplacement conditions can be obtained, as demonstrated by investigations at Axial Volcano on the Juan de Fuca Ridge. More comprehensive investigations of active basalt flows—both in nature and in the lab—are required to generate the next great leap in our understanding.

Buho seamount on the Galapagos Spreading Center (GSC) serves as a useful demonstration of both the current state of our knowledge, and the gaps in our present understanding. Buho is a flat-topped seamount approximately 2.6 km in basal diameter and ~250 m tall, located at 95°E, 2°N within the GSC. The seamount summit is composed of large (>3 m across) lobes that show little relief at their margins. The lobes are widest (≥5 m) near summit depressions that are interpreted to be vents; lobes are smaller distally. Major-element geochemistry gives a low lava viscosity (<100 Pa s). Combined with flow morphology, this suggests an effusion rate of ~10m³/s at the vent. At the break in slope that marks the edge of the summit, the lava flow morphology changes, but not as predicted. Simulations predict that increased underlying slope favors the formation of lava channels, but Buho’s flanks are composed of pillows and tallus. This implies that the tensile strength of basaltic crust partially controls submarine lava flow morphology, and this property is not well quantified on active flows.

To improve our understanding of submarine lava flow morphologies, we need detailed (~1 cm resolution) topographic surveys before and after eruptions so that the role of pre-flow topography and roughness can be quantified. Similar surveys after the eruption are required to obtain accurate estimates of final flow dimensions. Sample collection, with geochemical and petrologic analyses, provides vital constraints on eruption temperature, viscosity, and cooling rates. Recent efforts in using “real” lava in large-scale simulations are a magical opportunity we should grasp.