Photo: Algeria’s Tin Bider Impact Crater As Seen From Orbit
Algeria’s coast enjoys a Mediterranean climate with mild, wet winters. Inland, however, the terrain is mostly high desert where mountains and impermanent rivers interrupt sand seas. In this dry, rugged terrain rests a crater: Tin Bider. Geologists estimate that Tin Bider was formed in the last 70 million years, perhaps in the late Cretaceous or early Tertiary Period. Spanning 6 kilometers (4 miles), the crater sits at the southern end of a range of hills.
The Advanced Land Imager (ALI) on NASA’s Earth Observing-1 (EO-1) satellite captured this natural-color image of Tin Bider Crater on December 3, 2010. The desert surface appears in shades of tan, camel, beige, and brown. Sunlight leaves north-facing slopes in shadow. In fact, the angle of the Sun can play an optical illusion. The crater certainly looks as if it sits at a lower elevation than the surrounding land, but it doesn’t. The angle of sunlight is from the south, and Tin Bider actually rises above the land to the south, east, and west.
Depending on the extraterrestrial impact that creates a crater, the resulting structure may be simple or complex. The elevated position and concentric rings of Tin Bider suggest that its structure is complex. The rings may result from terraces composed of rock that collapsed after the impact. The underlying geology where the impact occurred, however, might also play a role. Land to the north of the crater is generally higher than land to the south.
