High-Silica Lava Morphology at Ocean Spreading Ridges: Machine-Learning Seafloor Classification at Alarcon Rise

Christina H Maschmeyer,Brian M Dreyer,David A Clague,Scott M White

doi:10.3390/geosciences9060245

Christina H Maschmeyer, Brian M Dreyer + Show 2 more

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https://doi.org/10.3390/geosciences9060245

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Abstract

The oceanic crust consists mostly of basalt, but more evolved compositions may be far more common than previously thought. To aid in distinguishing rhyolite from basaltic lava and help guide sampling and understand spatial distribution, we constructed a classifier using neural networks and fuzzy inference to recognize rhyolite from its lava morphology in sonar data. The Alarcon Rise is ideal to study the relationship between lava flow morphology and composition, because it exhibits a full range of lava compositions in a well-mapped ocean ridge segment. This study shows that the most dramatic geomorphic threshold in submarine lava separates rhyolitic lava from lower-silica compositions. Extremely viscous rhyolite erupts as jagged lobes and lava branches in submarine environments. An automated classification of sonar data is a useful first-order tool to differentiate submarine rhyolite flows from widespread basalts, yielding insights into eruption, emplacement, and architecture of the ocean crust.

Highlights

Seafloor produced at spreading ridges consists mostly of basaltic lava; more evolved rock compositions are not as rare as previously believed
We focused on lava flow scale with pixel-based classification, we integrated information at both scales with our neighborhood size of slope, bathymetric position index (BPI), and slope range
The resulting classification illustrates the distribution of lava flows with basaltic and rhyolitic submarine lava flows of intermediate composition observed elsewhere [13,14,27], the diameter and geomorphic characteristics (Figure 11)

Summary

Introduction

Seafloor produced at spreading ridges consists mostly of basaltic lava; more evolved rock compositions are not as rare as previously believed. The difficulty of locating these outcrops of non-basaltic rock types during the limited time and distance of deep-sea dives motivates this study to investigate alternate methods of prospecting for high-silica submarine lava types. Alarcon Rise, in the Gulf of California, is a unique ridge segment with lava flows with mafic, intermediate, and felsic compositions (Figure 1). The goal of this study was to determine whether morphology can be used to identify submarine lava flows of different compositions. Lava containing more silica is typically described as large pillows for andesite or dacite composition (e.g., [13,14]) (Figure 2). In 2012, the first spreading ridge rhyolites were discovered along a faulted ridge and breccia-covered mound in Alarcon Basin [15]

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