Structurally controlled regional groundwater circulation: Origin of geothermal springs in Sri Lanka

In the context of switching power generation towards renewable energy sources, the geothermal exploration of low enthalpy systems has gained interest also in regions with little to no recent tectonic or magmatic activity such as Sri Lanka. Sri Lanka has 9 low enthalpy systems with yet unknown heat generating mechanisms besides several existing hypotheses. Recent studies of such kind of low enthalpy geothermal systems hypothesize that fault network and recharge elevations are the main factors controlling the origin of the hot springs.

We studied the fault network, shear zones, and regional fracture networks to understand the heat flow causing the Sri Lankan hot springs. Remote sensing and geophysical methods were used to identify and analyze lineaments. We find that (1) The peak circulating temperatures of deeply circulating meteoric water depend on the elevation of the recharge zone for the corresponding hot spring. (2) Hot springs are formed in a terrain with a long fault / shear zone (starting from the highlands) when cross cuts with a regional fracture network occur in or near to the hot spring fields. (3) Highest number of hot springs in the country relates with the fault network that crosses the Mahaweli shear zone at the boundary of the two geological complexes Highland and Vijayan.

We conclude that the fault network that crosses both the central highlands and the Vijayan Complex plays a major role in the heating of deep percolating water, as it transports the water over more than hundred kilometers distance from the recharge zones to the hot springs.