It could very well be a volcanic crater, but the topography (i.e. alt.) also suggests an impact crater. If the island has a mysterious and powerful electro-magnetic field (EMF), would an asteroid be more likely to land there? It is possible that an interstellar comet bearing unique metals, (or even alien intelligence) may have caused the strange properties of the island.
Impact crater; Pretoria, S. Africa:
image from:
Department of Geology, University of the Witwatersrand
Private Bag 3, WITS 2050, South Africa
065wur@cosmos.wits.ac.zawww.saao.ac.za/~wgssa/as2/reimold.html