Most channels originated from jumbled, blocky terrain produced by collapse of the ground that formerly contained the discharged debris and water. At the terminus of the channels in the northern plains, expanses of sediments were deposited in temporary lakes that ultimately sublimated and disappeared. Overall geologic activity declined during the youngest, or Amazonian, period on Mars, but not before the major development of immense volcanoes on the Tharsis and Elysium rises. Most of the volcanoes form large shields having summit calderas and made up of basaltic lava flows, similar to the Hawaiian volcanos. Along the canyon walls of Valles Marineris, huge landslides dumped millions of tons of debris across canyon floors.
Wind continues to reshape the Martian surface.
Both polar plateaus appear to be made up of layered deposits of dust and ice that are easily eroded and redeposited by solar heating and wind. When Johannes Kepler determined in 1609 that the orbital path of Mars is elliptical, he abolished the older Ptolemaic theories based on circular orbits of the planets. The very next year, Galileo made the first telescopic observations of the planet and recorded its phases. In the late 1600s other scientists made closer observations of Mars, determining that its rotational period is close to Earth's, that it has polar caps that show seasonal change, and that dark areas could be distinguished. These were thought to be seas.