Before the dig, scientists had discovered large concentrations of metal under the ground around Rangoon's airport, lending support to the theory that up to 36 planes were buried there.

BBC: Search for 'buried Spitfires' in Burma called off

Such concentrations are usually created by geological events, such as volcanic eruptions and tectonic plate shifts that steer hot metal-bearing fluids into upper, accessible parts of the Earth's crust, erosion, or massive sedimentary movements.

WSJ: Exhausting the Earth's Resources? Not So Fast