The ship struck an extinct underwater volcano, which rose some 1,000 m (3,300 ft) above the surrounding abyssal plain, triggering a 2 km (1.2 mi) landslide. Bismarck slid down the mountain, coming to a stop two-thirds down. Ballard kept the wreck's exact location a secret to prevent other divers from taking artefacts from the ship, a practice he considered a form of grave robbing.[136]