Investigating the Lake Bosumtwi impact structure: Insight from numerical modeling

The current topography of the Lake Bosumtwi crater and some of its structural dimensions have been determined by geophysical methods. We combine these data with sophisticated numerical models to evaluate the cratering process itself (for example, melt and tektite generation) as well as to test the modeling code. The geophysical maps show some asymmetry in plan view, with the main anomaly north of the crater center. The simulations of the early stage show asymmetric patterns only in ejecta and tektite distributions, while the late stage is modeled for the vertical impact without any asymmetry. We estimate the projectile size from scaling laws and then, varying material properties, reproduce a crater, which is similar to the Bosumtwi, but too deep. Bulking allows us to reconcile differences between the model results and the observed topography. Shock melt estimates are in good agreement with the Bosumtwi magnetic signature. Modeled distribution of tektites assumes an impact angle of 30degrees-45degrees and an impact direction from the N-NE. The combination of numerical models and field evidence not only provides necessary information for upcoming scientific drilling of the structure but also suggests interesting and well-suited drill sites. Besides the central uplift and the annular moat with a suggested thick breccia cover, drilling at the location of the geophysical anomalies and comparison of downrange and transversal locations will provide new insight into preimpact and impact-induced asymmetries.