Impact structures
Crater cluster
Some bodies break up in the atmosphere and their pieces drift slightly off course. When they strike, they form a crater cluster.
Impacting bodies are exposed to strong pressure and heat. The smaller and weaker ones – that is, rubble-pile asteroids – break apart. The pieces differ in size and shape, so they follow slightly different paths. They strike partly overlapping or right next to one another.
Such impacts make craters a few kilometres across. These are not regular, bowl-shaped craters. They have irregular shapes and uneven floors, probably because the ejecta from the separate impacts pile up and the shock waves overlap.
On Earth, bodies that break up in this way make craters from a metre to 100 m across. Bodies that make larger craters reach the surface in one piece. Crater clusters on Earth are called crater fields (for example, the Henbury crater field in Australia). In the Chiemgau crater field in Bavaria, 80 Bronze Age craters are scattered over an area of 60 × 30 km.
The plate shows the Marianne crater cluster.
The figure shows the craters Erika (10.5 km across) and Sayligul (4.3 km across). Sayligul is a smaller multiple crater: the trace of a body that broke up during impact. Erika is a single crater, but it is irregular in shape and its floor is covered with coarse debris.
