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Massive submarine basalt flows were sampled at five sites on the Tristan‐Gough‐Walvis hotspot track in the South Atlantic by International Oceanic Discovery Program Expeditions 391/397T, where the plume was interacting with a mid‐ocean ridge, a setting similar to that the of modern Iceland. High resolution XRF core scans document significant internal chemical variations with depth in these flows. Some of this reflects basal olivine accumulation. However, some examples have “scallop‐shaped” patterns that are interpreted to represent influxes of new magma during flow lobe inflation with successive lava injections focused toward the base of the flow unit. Olivine concentration in the deeper parts of the flow is interpreted to reflect top‐down tapping of a vertically zoned magma chamber, with the upper part of the chamber erupting first, and successive eruptive pulses tapping progressively deeper levels of the stratified chamber. The occurrence of massive submarine lava flows requires high eruptive fluxes relative to pillow lava formation. Propagation of these massive flows is favored by (a) high sea water confining pressures, which inhibit vesiculation and keep effective viscosity low and dissolved volatile content high, and (b) chill zones and thick viscoelastic crusts of quenched lava on the flow tops, which effectively insulate the flow interior from ambient temperatures. The formation of a thin film of super‐heated steam on the upper flow surface may similarly enhance the insulation. Evidence suggests that similar massive flows on the seafloor may extend many kilometers from their vents.
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Vapor Bubbles and Velocity Control on the Cooling Rates of Lava and Pyroclasts During Submarine Eruptions
Abstract Investigating the conditions behind the formation of pyroclast textures and lava flow morphologies is important to understand the dynamics of submarine volcanic eruptions, which are hard to observe. The development of clast textures and lava morphologies depends on the competing effects of their eruption rates and the rates of solidification. While eruption rates are governed by subsurface magmatic processes, the solidification timescales depend on the rate of heat loss from lava to the external water. However, the effect of the speed of lava flow or clast on their solidification timescales under two‐phase (liquid water and vapor bubbles) water boiling conditions is poorly constrained. Using laboratory experiments with remelted igneous rocks, we investigate the effect of the relative motion between lava and external water on its cooling timescale. We use a range of water speed (0–12.5 cm s−1) in our experiments while keeping our sample stationary to simulate a range of relative speed between lava and ambient water. Using transient heat transfer modeling, we find that heat flux from the surface of the sample to the external water overall increases with increasing water speed. We find heat transfer coefficients of up to ∼1.72 × 103 W m−2 K−1. The implications of high heat flux on the formation of solid lava crust under submarine conditions are discussed.
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- PAR ID:
- 10420780
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Solid Earth
- Volume:
- 127
- Issue:
- 8
- ISSN:
- 2169-9313
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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