Evidence for long timescale (>10³ years) changes in hydrothermal activity induced by seismic events

Abstract

The pollen 14 C age and oxygen isotopic composition of siliceous sinter deposits from the former Beowawe geyser field reveal evidence of two hydrothermal discharge events that followed relatively low-magnitude (<M5) earthquakes of Holocene and late Pleistocene age along the Malpais fault zone in Whirlwind Valley, Nevada, USA. The observed 20‰ trend of decreasing d 18 O over about a 5000-to-7000-year period following each earthquake is consistent with a fault-controlled groundwater flow system that, following initial discharge of deep and hot groundwater, contains increasing amounts of cool meteoric water through time. Model simulations of this hydrothermal system can only match trends in the isotope data if we include a thousand-fold increase in fault permeability (from <10 À14 m 2 to >10 À11 m 2 ) following each earthquake. However, the timescale for onset of thermal convection implied by an overturned temperature profile in a geothermal well 300 m from the Malpais fault is much shorter: 200-1000 years. We speculate that individual segments of the Malpais fault become clogged on shorter timescales and that upward flow of groundwater subsequently follows new routes to the surface.

Topographic and Faults Control of Hydrothermal Circulation Along Dormant Faults in an Orogen

“…Hence, the recent and current low tectonic activity in the Eastern Pyrénées (see section ), together with fluid overpressure and favorably oriented stress field, or current seismicity, may suffice to maintain an efficient permeability in the fault entire network. In addition, our study highlights the importance of permeability variations along the Têt fault for the location and temperature of hot springs: (i) enhanced permeability at fault intersections as demonstrated by many previous authors (Belgrano et al, ; Faulds et al, ; Person et al, ) and (ii) the partial sealing of the Têt fault damage zone at Thues‐entre‐Valls (Taillefer, ), which could explain the lack of hot springs at places where numerical models predict a strong positive anomaly (Figure d, and see Howald et al, ). This suggests that permeability has not been constant throughout the faults (along strike and in depth) over the last 5 Ma.…”

The Fascinating and Complex Dynamics of Geyser Eruptions

“…The fields occur in areas of recent or active magmatism where the supply of heat is abundant, mostly at high latitudes where precipitation rates are high, and where glacial deposits overly SiO 2 -rich rhyolite flows or ignimbrites. Most formed following the last glaciation, as inferred by stratigraphy and the few radiometric dates of sinter deposits (Foley 2006, Jones et al 2007, Lynne et al 2008, Howald et al 2014, Lowenstern et al 2016. Some exceptions to this generalization include geysers along the East African rift system, mainly along the shores of Lake Bogoria in Kenya (Renaut & Owen 2005, McCall 2010, where geyser activity is not linked to rhyolitic volcanism.…”

Fault zone hydrogeology: introduction to the special issue

“…In many instances, hot spring discharge is focussed along deeply penetrating faults (Howald et al . ). The geochemistry, discharge rate and temperature of hot spring waters provide constraints on the circulation depth and fault zone properties.…”

“…Faults can act as vertical conduits providing pathways for fluid transport through the Earth's crust (Sibson 1981). In many instances, hot spring discharge is focussed along deeply penetrating faults (Howald et al 2015). The geochemistry, discharge rate and temperature of hot spring waters provide constraints on the circulation depth and fault zone properties.…”