Although the Galapagos are located on the equator, they are not exceedingly hot by tropical standards, with average daytime temperatures in the lowlands reaching about 85°F. The islands are usually quite dry and experience only a short rainy season. The climate is greatly influenced by the Pacific's Humbolt Current, which carries cool water from the Antarctic northward along the South American coast to the Galapagos.
The Galapagos Islands are located above a hotspot in the Earth's crust. This hotspot, also referred to as a mantle plume, is a column of heated rock that reaches from deep within the Earth's layers. The heated rock rises and as it does it decompresses and partially melts, forming magma.
The magma accumulates in the top layer of the earth (the lithosphere) where it forms magma chambers located a few kilometers below the surface. From time to time, magma chambers make their way to the surface and the result is a volcanic eruption.
Over the centuries, the magma plume under the Galapagos has forced the lithosphere upward and eruptions have thickened the crust. The result is a volcano that, in the case of the Galapagos, eventually grows tall enough to emerge from the surrounding ocean.
The Galapagos are similar to Hawaii, the Azores, and Reunion Island, which are also the result of mantle plumes.