The interior of most of the islands consists of undulating hills and plains, with a topography generally not exceeding above mean sea level. Wilson Island rises to 216 m. Occasionally the land rises reasonably abruptly from the sea to a domed plateau, and there are a few rocky coastal cliffs; however, in the main the coastlines are relatively flat, interspersed by both rocky and sand beaches and some low-lying lagoons and estuaries on the larger islands. Coral reefs surround many of the islands, particularly on the "sea-ward" (i.e., eastern) coastlines.