An assessment of hydrothermal alteration in the Santiaguito lava dome complex, Guatemala: implications for dome collapse hazards

Abstract

A combination of field mapping, geochemistry, and remote sensing methods has been employed to determine the extent of hydrothermal alteration and assess the potential for failure at the Santiaguito lava dome complex, Guatemala. The 90-year-old complex of four lava domes has only experienced relatively small and infrequent dome collapses in the past, which were associated with lava extrusion. However, existing evidence of an active hydrothermal system coupled with intense seasonal precipitation also presents ideal conditions for instability related to weakened clay-rich edifice rocks. Mapping of the Santiaguito dome complex identified structural features related to dome growth dynamics, potential areas of weakness related to erosion, and locations of fumarole fields. X-ray diffraction and backscattered electron images taken with scanning electron microscopy of dacite and ash samples collected from around fumaroles revealed only minor clay films, and little evidence of alteration. Mineral mapping using ASTER and Hyperion satellite images, however, suggest low-temperature (<150°C) silicic alteration on erosional surfaces of the domes, but not the type of pervasive acid-sulfate alteration implicated in collapses of other altered edifices. To evaluate the possibility of internal alteration, we re-examined existing aqueous geochemical data from dome-fed hot springs. The data indicate significant water-rock interaction, but the Na-Mg-K geoindicator suggests only a short water residence time, and δ 18 O/δD ratios show only minor shifts from the meteoric water line with little precipitation of secondary (alteration) minerals. Based on available data, hydrothermal alteration on the dome complex appears to be restricted to surficial deposits of hydrous silica, but the study has highlighted, importantly, that the 1902 eruption crater headwall of Santa María does show more advanced argillic alteration. We also cannot rule out the possibility of advanced alteration within the dome complex interior that is not accessible to the methods used here. It may therefore be prudent to employ geophysical methods to make further assessments in the future.

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

“…Where magma is rising slowly, permeable magma foam (Eichelberger et al, 1986;Jaupart and Allègre, 1991;Rust and Cashman, 2011), or cracked magma (Tuffen et al, 2003;Lavallée et al, 2013) allows outgassing along the outer shear margin of the magmatic column (Gaunt et al, 2014;Hornby et al, 2015) and/or out into the surrounding country rock, developing a partially or periodically open system (Castro et al, 2012;Cashman and Sparks, 2013;Kendrick et al, 2013). Evidence of continual outgassing and a periodically open system can both be observed at Santiaguito Bluth and Rose, 2004;Johnson, 2004;Holland et al, 2011;Scharff et al, 2012;Ball et al, 2013).…”

“…The outlines of units were based on high-resolution aerial orthophotographs taken in 2006 by the Instituto Geographico Nacional (IGN) of Guatemala. Features such as the outline of the main lava flows were adapted (in consultation with the authors) from Escobar-Wolf et al (2010) and Ball et al (2013). The focus of this study was on mapping summit features such as individual spines and lobes, their strikes and dips, and unique textural or structural features associated with them.…”

Acid‐Induced Dissolution of Andesite: Evolution of Permeability and Strength

“…Similarly, the failure strength of edifice‐forming rock (and other related mechanical properties) can dictate the potential for volcanic flank collapse and associated volcanic hazards. The capacity for edifice weakening or strengthening over time is thus an important consideration (e.g., Reid et al, ), and previous research has highlighted the important contribution of alteration to the strength and stability of volcanic edifice and dome structures (e.g., Ball et al, , ; Reid et al, ). In volcanic systems around the world, alteration‐induced edifice weakening has been related to consequent generation of potentially devastating collapse and flow phenomena (e.g., Carrasco‐Núñez et al, ; Cook et al, ; Houghton et al, ; Manville et al, ; Neall, ; Varekamp et al, ).…”

Volcanological applications of unoccupied aircraft systems (UAS): Developments, strategies, and future challenges

“…The timing of high-hazard events can be difficult to predict, with triggering processes effective over sub-minute timescales to years (e.g. column collapse due to eruption rate changes, or lava dome collapse from hydrothermal alteration [Ball et al 2013;Darmawan et al 2018b;Heap et al 2018]). Magma effusion rate, and its temporal variability, also affect lava flow runout lengths, along with topography over length scales down to decimetres [Dietterich et al 2015;Rumpf et al 2018].…”