Geography of Vanuatu
Vanuatu is a "Y" shaped archipelago of volcanic islands and submarine volcanoes in the South Pacific Ocean, stretching from 13.2' to 20.5' South to 166.2' to 170' East. The total number of islands exceeds eighty, though many are no more than small islets or rocky outcrops. Of these, there are thirteen major islands, nine home active volcanoes.
Vanuatu is 2,172 kilometers (1,303 miles) northeast of Sydney and 5,750 kilometers (3,450 miles) southwest of Honolulu. Fiji lies to the east, New Caledonia to the south, and the Solomon Islands to the northwest, all within the area of the South Pacific called Melanesia.
The northernmost island is Liu and lies just a few miles south of the Solomon's southernmost islands of Santa Cruz. Officially, Vanuatu's southern most island is Aneityum, however it also claims Mathew and Hunter Islands further to the south (disputed by New Caledonia).
These two islands are nothing more than a rocky outcrop and smoking volcano, but 'ownership' of them would extent the Maritime economic zone considerably, as Vanuatu claims an exclusive economic zone of 200 nautical miles. (Territorial sea: 12 nm).
The total land mass of the island group is just over 14,760 square kilometers (5,697 square miles) with the two largest islands, Espiritu Santo and Malekula taking up nearly one-half of the total land area. Total coastline is 2,528 kilometres, about the same as French Polynesia.
The capital, Port Vila is located Longitude 17.45S and Latitude 168.18E.
The climate of Vanuatu is tropical, moderated by southeast trade winds from around May to September each year. Rainfall averages about 2,360 millimeters (94 in.) per year but can be as high as 4,000 millimeters (160 in.) in the northern islands.
Tropical cyclones (typhoons or hurricanes) threaten the islands from December through March, with the occasional early cyclone in mid November. Generally, cyclones later in the season are stronger. Other natural hazards include volcanic eruptions, mudslides from these and heavy rainfalls and frequent, generally minor earthquakes.
Geologically, Vanuatu lies along the area known as the Pacific Ring of Fire. The oldest islands, Espiritu Santo and Malekula are on the left side of the Y shape of the archipelago. Though these two islands have no volcanoes, they are made of Miocene (5-24 million years old) andesitic volcanic rocks resulting from the northeast ward directed subduction of the Australian Plate beneath the edge of the Pacific Plate.
In fact the entire island chain owes its existence to the active volcanism resulting from these two plates converging at a rate of around 9 cm per year. Overall Vanuatu is uplifted around 4 cm per year. There is also a divergent plate boundary (called a spreading center or spreading axis) east of Vanuatu, adding to the complex geology of the region. For further information see volcanoes.
As volcanoes growing beneath tropical waters come close to the surface, coral animals build reefs on them. When the volcanoes rise above the surface of the water to become islands, the coral dies and forms limestone. Coral growth tends to follow the shape of the land, so lava tunnels, caves and fissures caused by volcanoes remain hollow, rather than filled with sediment, with layers of coral growth building on their walls. When the islands rise above the water, the dead coral, limestone, is covered in soil as plants take hold. But it will also erode away as water trickles beneath the soil and dissolves the calcium out of the limestone. Limestone caves form because of this.
Most of the volcanic eruptions in Vanuatu are Plinian, resulting in huge expanses of thick ash, later cemented together by rainfall. Thus the geology of the Vanuatu is basically basalt, from the build up of the shield volcanoes and lava flows, with overlays of limestone from coral buildup and compacted ash from eruptions.
Vanuatu is rich in both underwater and underground caves formed both by volcanic activity and the erosion of limestone and the much softer ash. Some caves, such as those at Siviri, on Efate Island, stretch inland for miles and their true extent has yet to be explored.
In recent years a huge series of underground fresh water caves has been discovered in Santo and is fast becoming popular with divers (see Dive Operators).
Other caves are filled with fascinating bat colonies or ancient cave drawings.
The most unusual aspect of the local geology is the formation of beach rock. In the high rainfalls of tropical climates, the calcium carbonate from shells and the skeletons of dead zoo plankton that make up the beach sediment can precipitate into a solution (dissolve). This solution gravitates down the beach to the littoral zone (area between high and low tide) and in the high temperatures of the tropical sun, the water evaporates. The calcium carbonate remains as a natural cement, welding together everything within the littoral zone, forming what is known as beach rock.
In places like Espiritu Santo this beach rock has welded not only sand, but the remains of W.W.II machinery dumped at places like Million dollar Point, into one huge long beach of naturally cemented war refuse. It's an amazing sight for not only war machinery was dumped here. Million Dollar Point may well have the distinction of being the only beach in the world made from rock embedded with tens of thousands of Coca Cola and 7 Up bottles.
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