203 Old and the New, Long and the Short: Perspectives on Integration of Timescales of Magmatic Processes: Special Session Related to MGPV Awards to Madison Myers and Anita Grunder

We encourage papers that challenge and give insights into the interplay between timescales, methodologies, and processes to build a cohesive understanding of the lifespan, evolution, storage, and eruption of magma, from plutonic to volcanic systems.

Tuesday, 21 October 2025
1:30 PM - 5:30 PM
HBGCC, 216AB

Post-emplacement vesiculation in monogenetic basaltic lava flows may cause emplacement timescales to be overestimated

Paper number: 203-6
Program: Technical Sessions
Time: 3:00 PM – 3:15 PM

Authors

Abstract

Lava flow thickness is used in estimating their volume and properties such as yield strength and viscosity, which can be used to constrain effusion rate and emplacement duration. However, lava flow thickness can change during or shortly after emplacement. Here we examine inflation resulting from post-emplacement vesiculation of two basaltic andesite lava flows in the Atacama desert, Chile. Both flows exhibit crease structures, which form when the brittle lava surface extends, producing cracks that can penetrate downwards into the ductile region of a flow, exposing confined lava to atmospheric pressure and triggering vesiculation and surface uplift.

Volcan San Pedro is a stratovolcano with a ~12km long lava flow. Crease structures form along the axes of flow lobes that are ~86m thick. The NW corner of the intersection of two orthogonal crease structures is the highest point on this lowermost section of the flow, rising ~126m above the desert. This suggests ~40m of inflation from the second crease, and that the pre-vesiculation thickness may have been less than 50m during emplacement. We have also documented crease structures in basaltic andesite flow lobes at La Poruña, a monogenetic cinder cone just a few km away.

The amount of inflation depends on the thickness of the layer that is able to vesiculate (which must be above the brittle-ductile transition), and the amount of bubble growth (controlled by nucleation and diffusion kinetics, ambient surface pressure, and the ability of the lava to maintain overpressure in bubbles). For closed-system vesiculation, exsolution of 0.01 or 0.1 wt.% H2O leads to a local volume increase of 1.7 times or 17 times respectively. At least half the thickness of many flows is either basal breccia or cooled upper crust. A 50 m thick flow, containing a vesiculating layer initially 20 m thick, could inflate by 34 m with exsolution of only 0.01 wt.% (100 ppm) H2O, for a post-vesiculation thickness of 84 m. Inflation would less if the flow were initially vesicular, or if degassing was through connected cracks rather than isolated bubbles, and greater if more than 0.01 wt.% H2O were exsolved. Changes in flow thickness due to inflation will affect the calculated values of flow volume, yield stress, viscosity, and emplacement duration, all of which will be overestimated. 

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-413919

© Copyright 2025 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.