Like many other island groups in the Pacific, the Marquesas Islands passed over, and were created by, an oceanic hotspot. A hotspot is generally found beneath the ocean's crust, and is fed by convective heat rising through the Earth's mantle. This heat melts the magma, which gets forced out through fractures in the oceanic crust and undersea volcanoes
It is thought that the islands and seamounts of the Marquesas were formed around 2.5-1.5 million years ago. They consist of two island groupings - North and South. Scientists have tracked the progress of the the islands over the hotspot, and have ascertained that the southeastern islands to are youngest. It's thought that the Marquesas hotspot plume could still active underwater.
Exposed to the forces of erosion the islands have been sculpted into dramatic landscapes with deep, narrow valleys separated by steep ridges that radiate from the eroded summits of the volcanos. The culture and identity of the Marquesans have been shaped by this unusual, and rather inhospitable, topography.