Bolide Crater Formation

Normal Fault

When a bolide first strikes Earth's surface, the force is so great that it carves through much of the underlying rock layers. The impact creates normal faults throughout the crater. The heat generated from the force of impact melts the underlying rocks, allowing them to flow through the fractures within the crater. Eventually these fluidized rocks settle and cool among the surrounding rock layers. Often the impact force will destroy the bolide itself, quickly leaving a void within the impact crater. In the case of a marine impact such as the Alamo Impact Event, this void is quickly filled with fragmented rock materials and water. The rush of water back into the void creates a strong current that carries both impact-related and new far-reaching material towards the crater. Over time, the crater is refilled with fragmented rocks as the walls collapse and slide back into the crater itself.

Depending on the size of the bolide, either simple or complex craters can form. Simple craters display a bowl-shape most often associated with impacts, whereas complex craters contain diverse topography throughout the crater. The Alamo Impact is associated with a complex crater comprising a variety of high rims and low troughs within it.