Geophysical characterization of hydrothermal systems and intrusive bodies, El Chichón volcano (Mexico)

Abstract

[1] The 1982 explosive eruptions of El Chichón volcano (Chiapas, Mexico) destroyed the inner dome and created a 1-km-wide and 180-m-deep crater within the somma crater. A shallow hydrothermal system was exposed to the surface of the new crater floor and is characterized by an acid crater lake, a geyser-like Cl-rich spring (soap pool), and numerous fumarole fields. Multiple geophysical surveys were performed to define the internal structure of the volcanic edifice and its hydrothermal system. We carried out a high-resolution ground-based geomagnetic survey in the 1982 crater and its surroundings and 38 very low frequency (VLF) transects around the crater lake. A 3-D inversion of the ground-based magnetic data set highlighted three high-susceptibility isosurfaces, interpreted as highly magnetized bodies beneath the 1982 crater floor. Inversion of a digitized regional aeromagnetic map highlighted four major deeply rooted cryptodomes, corresponding to major topographic highs and massive lava dome outcrops outside and on the somma rim. The intracrater magnetic bodies correspond closely to the active hydrothermal vents and their modeled maximum basal depth matches the elevation of the springs on the flanks of the volcano. Position, dip, and vertical extent of active and extinct hydrothermal vents identified by VLF-EM surveys match the magnetic data set. We interpret the shallow lake spring hydrothermal system to be mostly associated with buried remnants of the 550 BP dome, but the Cl-rich soap pool may be connected to a small intrusion emplaced at shallow depth during the 1982 eruption.

Combining Multiphase Groundwater Flow and Slope Stability Models to Assess Stratovolcano Flank Collapse in the Cascade Range

“…A central cylindrical intrusion is built into each scenario but may or may not inject heat and mass into the edifice, depending on the scenario (pre‐intrusion or post‐intrusion). Simulation scenarios (Figure ) have been simplified significantly to investigate effects of different structures; in reality, stratovolcanoes contain a combination of many nonsymmetric structures, such as alternating layers of lava flows and pyroclastic material/breccia, old lava domes, old craters collapse scars, and dikes (Acocella & Neri, ; Belousov et al, ; Cecchi et al, ; Jutzeler et al, ; Siebert, ).…”

A photographic method for detailing the morphology of the floor of a dynamic crater lake: the El Chichón case (Chiapas, Mexico)

“…Nevertheless, besides minor rock fall and mass movement from the S and SW sector of the El Chichón crater in 1986-1987, no strong morphological changes that could have affected the morphology of the crater lake basin occurred after the 1982 eruptions. A recent geophysical survey (Jutzeler et al 2011) demonstrates the absence of a remnant magma body beneath the 1982 crater, which excludes any influence of a possible magmatic system on the crater lake morphology. Based on these facts, it is very probable that the El Chichón crater lake has always been a rather shallow lake since its formation in 1982, undergoing only minor morphological variations due to sediment washing into the lake since then.…”

“…The initially magmatic crater lake (pH *0.5, Cl *24,000 mg/l, TDS *34,000 mg/l, and T *55°C; Casadevall et al 1984) converted into a hydrothermal-dominated system (pH *1.8-2.5, TDS \3,000 mg/l, and T \ 42°C; Taran et al 1998) (1988. Despite the fact that the eruptions breached the former hydrothermal system, leaving a 1-km wide 200-m deep crater, there is currently no clear evidence for the presence of a brecciated diatreme beneath the crater floor (Jutzeler and Varley 2008;Jutzeler et al 2011). There is great uncertainty over the depth of the 1982 crater lake, though it is presumed that the maximum depth was 120 m, and that the lake has a funnel-shaped morphology (Casadevall et al 1984).…”

Geochemical monitoring of volcanic lakes. A generalized box model for active crater lakes

“…Structural mapping using CO 2 flux surveys on and around crater lakes can give qualitative insights into the fluid migration regimes Taran 2009, Mazot et al 2011]. Geophysical surveys (self potential, resistivity, magnetometry, microgravimetry) can increase the knowledge of the seepage regime of crater fluids [Fournier et al 2004, Rymer et al 2009, Fournier et al 2010, Jutzeler et al 2011]. These indirect approaches, however, do not help to quantify the seepage output flux.…”