Textural Insights Into the Evolving Lava Dome Cycles at Santiaguito Lava Dome, Guatemala

Abstract

The structures and textures preserved in lava domes reflect underlying magmatic and eruptive processes, and may provide evidence of how eruptions initiate and evolve. This study explores the remarkable cycles in lava extrusion style produced between 1922 and 2012 at the Santiaguito lava dome complex, Guatemala. By combining an examination of eruptive lava morphologies and textures with a review of historical records, we aim to constrain the processes responsible for the range of erupted lava type and morphologies. The Santiaguito lava dome complex is divided into four domes (El Caliente, La Mitad, El Monje, El Brujo), containing a range of proximal structures (e.g., spines) from which a series of structurally contrasting lava flows originate. Vesicular lava flows (with a'a like, yet non-brecciated flow top) have the highest porosity with interconnected spheroidal pores and may transition into blocky lava flows. Blocky lava flows are high volume and texturally variable with dense zones of small tubular aligned pore networks and more porous zones of spheroidal shaped pores. Spines are dense and low volume and contain small skeletal shaped pores, and subvertical zones of sigmoidal pores. We attribute the observed differences in pore shapes to reflect shallow inflation, deflation, flattening, or shearing of the pore fraction. Effusion rate and duration of the eruption define the amount of time available for heating or cooling, degassing and outgassing prior to and during extrusion, driving changes in pore textures and lava type. Our new textural data when reviewed with all the other published data allow a cyclic model to be developed. The cyclic eruption models are influenced by viscosity changes resulting from (1) initial magmatic composition and temperature, and (2) effusion rate which in turn affects degassing, outgassing and cooling time in the conduit. Each lava type presents a unique set of hazards and understanding the morphologies and dome progression is useful in hazard forecasting.

Progressive Growth of the Cerro Bayo Cryptodome, Chachahuén Volcano, Argentina—Implications for Viscous Magma Emplacement

“…Despite this rapid emplacement, lava dome growth is often cyclic and characterized by a range of different magma extrusion types with resulting structures that include lava flows, breccias, shear zones, and spines (Ashwell et al, ; Cashman & Taggart, ; Moore et al, ; Sparks et al, ). These different structures have been attributed to differences in extrusion rate, composition (Cashman et al, ; Fink & Griffiths, ; Watts et al, ), volatile content (Anderson & Fink, ), stress conditions during emplacement (Hale & Wadge, ), fragmentation processes (Wadge et al, ), sintering (Kendrick et al, ; Vasseur et al, ), as well as magma viscosity changes (Rhodes et al, ). In cryptodomes and laccoliths, growth produces internal contacts or heterogeneities due to sill stacking (de Saint‐Blanquat et al, ; Wilson et al, ) and deformation of older emplacement structures, such as doming of flow bands or fractured bands due to successive inflation (Mattsson et al, ).…”

“…A strain-and strain rate-dependent rheology of the magma can therefore cause the viscosity to dramatically increase, which can lead to viscous stalling of parts of the magma body (Mattsson et al, 2018;Pistone et al, 2016). Another process that may increase magma viscosity and lead to viscous stalling is porosity reduction by compaction and pore collapse or passive degassing through a fracture network (Ashwell et al, 2015;Heap et al, 2015;Kennedy et al, 2016;Kushnir et al, 2017;Rhodes et al, 2018). Since vesicles are sparse in Cerro Bayo, permeability was likely dominantly created by fracturing of the magma (cf.…”

“…In active volcanoes, cryptodome formation can be studied through surface deformation and seismic monitoring (Minakami et al, 1951;Okada et al, 1981). However, the internal dynamics of the intruding magma are hidden and our understanding is mostly based on observations during lava dome extrusion, such as at Unzen, Japan, Mount St. Helens, Soufrière Hills, Montserrat, and Santiaguito, Guatemala (Cashman & Taggart, 1983;Moore et al, 1981;Nakada et al, 1995;Rhodes et al, 2018;Sparks et al, 2000).…”

“…Another way to understand cryptodome emplacement is the study of exposed and extinct solidified volcanic domes, cryptodomes, and laccoliths (Ashwell et al, 2018;Goto & McPhie, 1998;Goto & Tomiya, 2019;Mattsson et al, 2018;Rhodes et al, 2018;Stewart & McPhie, 2003). The study of structures within and around such intrusions provides insights into the dynamics of their emplacement and can reveal potential weakness zones in the intrusion.…”

Topographical controls on small‐volume pyroclastic flows

“…Petrographic evidence from the obsidian blocks and fiamme reveals that there is a complete textural gradation in terms of crystal content, vesicularity and plasticity, thereby suggesting a textural gradation similar to that expected from the carapace to the interior of lava domes (e.g. Nakada & Motomura, ; Rhodes et al ., ). It is also worth mentioning the presence of banded pumice and a mixed phenocryst assemblage as a characteristic feature of the Arico ignimbrite (Alonso et al ., ; Bryan et al ., ,b; Brown et al ., ).…”