The island is a series of gravel bars connecting volcanic bedrock islands. The volcanism is not recent and may be millions of years old. The crescent shaped island may be the result of an eroded caldera similar to the much more recent Deception Island volcano complex. The parallel gravel bars are a result of post-glacial uplift of the area after the much larger Pleistocene ice cap melted and the pressure was released.
Wildlife
Plants found on the island include several lichen and moss species as well as Antarctic Hairgrass. The island has been identified as an Important Bird Area by BirdLife International because it supports a breeding colony of about 100 pairs of south polar skuas. Other birds nesting on the island include chinstrap penguins, Antarctic terns, kelp gulls, Wilson's and black-bellied storm petrels, Cape petrels, brown skuas, snowy sheathbills and imperial shags. Weddell and Antarctic fur seals regularly haul out on the beaches. Southern elephant seals have been recorded. Whales are often seen patrolling the shores.
Access
The island is used as a stop during Antarctic cruises, with the peak of visitation during November–March. There is a walking track on the southern part of the Island which allows tourists to get a close view of the wildlife, and of the surrounding mountainous scenery of nearby Livingston and Greenwich Islands. The path begins on the south side of Menguante Cove, runs westwards along the beach to Cámara Base, then turns north along the head of Menguante Cove, and eventually ascends northeastwards to the top of Xenia Hill.
In September 2010, Google added Street View imagery of Half Moon Island to its Google Earth and Google Maps services. The expansion of Google Street View onto the island means all seven continents had imagery through the service. As the island has no roads, the images appear to have been taken with a camera on a tripod. The shadow of the photographer can clearly be seen if one were to move the view so as to look at the ground. Also, the iconic Pegman from Google was replaced with a Penguin, due to the island's use as a breeding colony by them. The penguin has since been changed back to Pegman.
Maps
from the exploration of the sloop Dove in the years 1821 and 1822 by George Powell Commander of the same. Scale ca. 1:200000. London: Laurie, 1822.