Macquarie Island is a geological wonder. The rocks hidden under its tussocks and peat were formed on or deep below the seabed. This makes the island unique and the main reason for its listing as a site of World Heritage significance.
Rock outcrops on the northern part of the island have been pushed up from about 6 km below the ocean floor, producing a unique exposure of rocks from the upper mantle. No drill hole has ever penetrated these depths and these exposures provide a rare opportunity for geologists to gain an understanding of such rocks. The southern part of Macquarie Island is composed of rocks formed by lava erupting from long fissures across the ocean floor. Mid-oceanic ridges like these are exposed in very few places, such as Macquarie Island and Iceland.
Small earth tremors frequently shake Macquarie Island and larger quakes measuring 6.2 or higher on the Richter scale average one a year.
Introduced Pests and the Macquarie Island Pest Eradication Project
Macquarie Island has a long history of battling the impacts of introduced pests.
The weka, or Maori hen, was brought to Macquarie Island in 1867 from New Zealand as a source of food. The weka put pressure on the native Macquarie Island parakeet and rail, and the species became extinct on the island. Weka numbers declined in the 1980s and the last weka was dispatched in 1988.
Feral cats were recorded as early as 1820. Colonies of ground and burrow-nest birds were easy prey for the proficient hunters and large numbers of them were destroyed within a few decades. Cat control measures were implemented in 1974, but it wasn't until the late 1990s that the focus shifted to complete eradication. Between 1998 and 2002 the intensive shooting and trapping program was successful in eradicating feral cats.
Rabbits were brought to the island in the late 1870s as a food source for the oiling crews working on the island. They eventually colonised the steep, soft-soiled hillsides and the plateau regions and the impacts of rabbit grazing on vegetation and soil stability became severe.
After several years of detailed planning, in 2007 funding was provided to implement an eradication plan that would simultaneously target mice, ship rats and rabbits. The project involved an extensive phase of aerial baiting, which was completed in July 2011. The last rabbit was recorded on the island in November 2011, and after three years of intensive patrolling with by hunting teams and their dogs, the project was declared a success in 2014.
With the removal of rabbits and the resulting intensive grazing pressure, the island's vegetation is rapidly rebounding. Sea birds, which had suffered predation of eggs and chicks by rats, are also returning in numerous areas. Invertebrates too, are recovering.
Macquarie Island Nature Reserve - Marine area
The Macquarie Island Nature Reserve also occupies all of Macquarie Island's State waters from 0-3 nautical miles outward, and is about 75,000 ha in size.
The island and surrounding area are unique in their geological characteristics. It is the only known location where oceanic crust, from a normal mid-ocean ridge, has been lifted above sea level in a major oceanic basin. Moreover, its overall north-south trend means that it acts as a major barrier to the Antarctic Circumpolar Current, the earth's largest and most important oceanic current, which flows eastward about the Antarctic landmass. This impacts on the balance of oceanic and atmospheric heat and chemical exchange, which in turn has an effect on the southern hemisphere's weather patterns.