Cape d’Ambre, the northernmost point of land on Madagascar (the world’s fourth largest island), is easily identified by its arrowhead shape. Diégo-Suarez Bay, the large natural bay along the northeast coast, is considered one of the finest natural harbors in the world. The bay, protected by a narrow inlet that provides shelter from strong Indian Ocean winds is believed to be the result of a submerging coastline or drowned river valley that formed many peninsulas around the bay. The very dark southern area is a small vegetated mountain range with elevations that exceed 4000 feet (1220 meters) above sea level. The area, known as the Ankarana Plateau, is composed of limestone rocks. With an average annual rainfall of 70 inches (180 centimeters), the underlying rocks are susceptible to erosion, thereby producing caves and underground streams—a karst topography. The rugged relief and the dense vegetation have helped protect the region from human intrusion.