While the "Beagle" surveyed the coasts of South America from February 1832 to September 1835, Darwin made several trips inland and found extensive evidence that the continent was gradually rising. After witnessing an erupting volcano from the ship, he experienced the 1835 Concepción earthquake. In the following months he speculated that as the land was uplifted, large areas of the ocean bed subsided. It struck him that this could explain the formation of atolls.