Elastic Flexure of Young, Overlapping Basaltic Lava Flows Offshore the Galápagos and Hawaiian Islands: Observations, Modeling, and Thermal/Chronological Analysis

Abstract

A recent multibeam bathymetry survey in the Galápagos archipelago revealed a novel observation between the islands of Santa Cruz and Santiago: a steep flexural moat formed between two volcanic flows, nearly 50 m deep and about 500 m wide. Submarine observations and elastic plate modeling are consistent with this feature forming after one inflationary flow overlapped another young flow, deflecting the underlying lava flow in what appears to be a classical elastic flexural pattern. We present a flexural analysis of this moat feature using a thin‐plate approximation to determine the effective elastic thickness of the underlying flow. Moreover, we propose that this elastic thickness serves as a proxy for the thickness of the cooling, solidifying upper crust of the lava flow at the time of deflection, a time‐dependent thermal property. This approach offers a chronological tool to put bounds on the elapsed time between two overlapping lava flows. We applied this method to the Galápagos moat to constrain the time history of its formation. Additionally, we identified and modeled seven additional flexural moat candidates in the Hawaiian archipelago and in the Galápagos using multibeam bathymetry. Elastic/thermal history analysis of these features yields relative time intervals between submarine lava flows ranging from a few years to about 600 years, which suggests that there is a critical time interval during which elastic deflection of the underlying lava flow may become “frozen in.” This methodology may provide helpful constraints on the temporal relations between overlapping lava flows wherever they form in relatively rapid succession.

Monogenetic Near‐Island Seamounts in the Galápagos Archipelago

“…Only one submarine sample is separated from the other seamounts in the region at the greatest Wards Distance (DR373), suggesting it is the least similar to other seamount lavas. This sample was not actually collected from a seamount, but instead from edge of a large lava flow emanating from the northwest (Abbott & Richards, 2020) that may be related to Santiago. This sample is the most similar in composition to a few lavas erupted on the western edge of Santiago and to lavas erupted on Isabela and Santa Cruz.…”

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

“…It is similarly challenging to distinguish between in parallel and in sequence flows based on field volcanological observations alone without detailed textural analysis. One potential distinguishing feature may be the 2D shape of the bottom flow lobe in an in parallel flow since it will be viscoelastically deformed by the load from the overlying flow lobe (Abbott & Richards, 2020). One consequence of this would be the formation of squeeze‐up structures at flow lobe edges seen in some CFB flow edges, for example, for the Western Ghats and the Rajahmundry Trap flows in the Deccan CFB (Dole et al., 2020; Fendley et al., 2020).…”

Some lava flows may not have been as thick as they appear

“…It is similarly difficult to distinguish between in parallel and in sequence flows based on field volcanological observations alone without detailed textural analysis. One potential distinguishing feature may be the 2D shape of the bottom flow lobe in a in parallel flow since it will be visco-elastically deformed by the load from the overlying flow lobe (Abbott & Richards, 2020). One consequence of this would be formation of squeeze-up structures at flow lobe edges seen in some CFB flow edges (e.g., Dole et al, 2020;Fendley et al, 2020b, for the Western Ghats and the Rajahmundry Trap flows in the Deccan CFB respectively).…”