Using Thermal Springs to Quantify Deep Groundwater Flow and Its Thermal Footprint in the Alps and a Comparison With North American Orogens

Elco Luijendijk,Christoph von Hagke,Saskia Köhler,Jacek Scibek,Grant Ferguson,Theis Winter

doi:10.1029/2020gl090134

Abstract

AbstractThe extent of deep groundwater flow in mountain belts and its thermal effects are uncertain. Here, we use a new database of discharge, temperature, and composition of thermal springs in the Alps to estimate the extent of deep groundwater flow and its contribution to the groundwater and heat budget. The results indicate that thermal springs are fed exclusively by meteoric water and make up 0.1% of the total groundwater budget. Spring water circulates on average to a depth of at least 2 km. The net heat extracted from the subsurface equals 1% of the background heat flow, which equals an average thermal footprint of 7 km2. Cooling by downward flow and heating by upward flow are three and two times higher than the net heat flow, respectively. Comparison with North American orogens shows that hydrothermal activity is higher in areas with high relief or areas under extension.

Highlights

Deep groundwater flow in mountain belts can affect fault strength (Hubbert & Rubey, 1959; Wintsch et al, 1995) and heat flow (Bodri & Rybach, 1998; Whipp & Ehlers, 2007) and may connect deep and shallow biospheres (Pedersen, 1993; Walvoord et al, 1999)
Our analyses suggest that thermal springs are fed by meteoric water and the discharge of the springs comprises 0.1% of the total meteoric groundwater budget of the Alps
Spring heat flux is underestimated because no discharge data were available for 32% of the thermal springs in the Alps

Summary

Introduction

Deep groundwater flow in mountain belts can affect fault strength (Hubbert & Rubey, 1959; Wintsch et al, 1995) and heat flow (Bodri & Rybach, 1998; Whipp & Ehlers, 2007) and may connect deep and shallow biospheres (Pedersen, 1993; Walvoord et al, 1999). Groundwater can penetrate large parts of the crust, as shown by stable isotopes of fault minerals (Person et al, 2007; Poulet et al, 2014) and 3He/4He ratios in thermal springs (Hoke et al, 2000; Karlstrom et al, 2013; Umeda et al, 2007). In contrast to sedimentary basins, where borehole data have yielded information on the volume, composition, and age of deep groundwater (Ferguson et al, 2018; Gleeson et al, 2016; Jasechko et al, 2017), data on the extent of deep groundwater flow in orogens are relatively scarce. Data from thermal springs have suggested that in parts of the Himalayas

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