The lake occupies a continental-scale
graben formed by SWS-ENE normal faults that have resulted in down-dropping the bottom of the lake to below mean sea level. Preservation of younger lithostratigraphic units within the graben form reverse stratigraphy with older units exposed at higher topographic elevations to the south. The graben channeled mountain glaciers which formed terminal moraine helping to modify the present-day shape of the lake. The tectonic activity that formed the depression can be inferred to subduction of the triple joint that has occurred over the past 20 million years, as indicated by ripple marks in volcaniclastic sediments observed along the southern shoreline. There is some speculation on whether the tectonics and
crustal heat flow in the lake area are influenced by the
asthenospheric window that exists beneath the crust in this region of Patagonia. The Marble Caves, Marble Chapel, and Marble Cathedral are unusual geological formations located on the shoreline midway along the lake's length. They represent a group of caverns, columns, and tunnels formed in monoliths of marble. The Marble Caves have been formed by wave action over the last 6,200 years. The northwestern shores have valuable mineral deposits of
lead and
zinc which were exploited intermittently from 1931 to 1996 in Puerto Cristal. There are various
river deltas on the lake's shores and some of them have older parts that are raised showing ivendence of higher lake levels in the past. The three main deltas lie at the outlet of the rivers Maitenes, Aviles and
Jeinimeni on the southern shores. == Gallery ==