Formation conditions and ejecta characteristics of Lonar crater (India): Constraints from photogrammetry, GPR and iSALE-2D

Formation conditions of impact craters in volatile-bearing targets and the emplacement mechanisms of their ejecta blankets remain poorly constrained [1, 2]. Terrestrial impact structures formed in basaltic targets provide an opportunity to link crater-scale morphology, ejecta characteristics, and subsurface structure to impact parameters and target properties under well-constrained conditions [3].

Lonar crater (India), formed in the Deccan Traps, preserves a relatively well-developed ejecta blanket and associated surface and subsurface structures. We reevaluate the geomorphology and subsurface architecture of Lonar crater to constrain primary impact conditions (trajectory, energy, target saturation and cratering efficiency), while assessing the origin of the nearby “little Lonar” structure as a secondary objective.

We use drone-based photogrammetry (DEMs complemented by TanDEM-X data), ground-penetrating radar (GPR), and petrographic analysis as independent approaches, alongside iSALE-2D numerical simulations constrained by the observed topography.

Previous geomorphological analyses indicate distal thickening of the ejecta blanket and flow-like surface textures. Field observations suggest laterally variable internal layering of the ejecta [4], which is supported by GPR data showing heterogeneous subsurface structures and strong variations in signal attenuation.

Our reevaluation focuses on excavation depth, transient cavity geometry, ejecta extent, crater polygonality and micro-fracture networks. Best-fit iSALE simulations reproduce a transient cavity of ~1.4 km diameter and ~530 m depth, evolving into the present ~1.9 km diameter crater, with peak shock pressures of up to ~10 GPa at the crater floor. These results provide a quantitative framework linking observed structural features to impact energy and target conditions.

Comparison with the Ries crater (Germany) indicates two distinct ejecta units and comparable stratigraphic relationships. Within this framework, the “little Lonar” structure shows disrupted subsurface geometries and possible normal faulting, consistent with formation in unconsolidated ejecta, although a binary impact scenario cannot be excluded.

[1] Osinski et al. 2011 Earth and Planetary Science Letters 310, 167–181. [2] Weiss and Head 2018 Meteoritics & Planetary Science 53, 741–777. [3] Wulf et al. 2019 Earth and Planetary Science Letters 506, 209–220. [4] Kumar et al. 2014 JGR Planets 119, 2029-2059.