Drainage systems of Lonar Crater, India: Contributions to Lonar Lake hydrology and crater degradation

Lonar, a 1.8-km-diameter impact crater in India, is a rare example of terrestrial impact craters formed in
basaltic bedrock. The estimated age of the crater ranges widely from less than 12 ka to over 600 ka, but
the crater preserves a relatively pristine morphology. We conducted a study of various drainage systems
of Lonar Crater. The crater floor hosts a shallow 5-m-deep lake, which fluctuates seasonally. Our
investigation reveals that the lake level is influenced by surface runoff that is active during the monsoon
and groundwater input effective during both the rainy and the dry seasons. The groundwater discharge is
observed as springs on the inner rim walls corresponding to weathered vesicular basalt and/or proximal
ejecta, which are underlain by thick massive basalt layers. This observation indicates that groundwater
movement is lithologically controlled: it passes preferentially through permeable vesicular basalt or
proximal ejecta but is hindered in less permeable massive basalt. It is hypothesized that groundwater is
also structurally controlled by dipping of basalt layers, interconnectivity of the permeable lithologic units
through fractures, and preferential pathways such as fractures within the permeable lithologic units.
Investigation on hydrological processes at Lonar Crater and its lake could provide useful insights into
purported paleo-crater lakes presumably formed in the basaltic crust of Mars. The Lonar Crater interior
shows signs of degradation in the forms of gullies and debris flows, and the Dhar valley incising in the
rim leading to form a fan delta. The ejecta surface is characterized by the presence of channels,
originating from the rim area and extending radially away from the crater center. The channels probably
resulted from surface runoff, and its erosion contributes to the removal of the ejecta. Lonar Crater is a
valuable analog site for studying degradation processes with potential application to impact craters
occurring on hydrologically active ancient Mars, or to other impact craters on Earth.