Lord Howe Island, Tasman Sea, Australia

Location: 31.5S, 159.1E
Elevation: 2,870 feet (875m)

Lord Howe Island is the erosional remnant of a 6.9 million-year old shield volcano. Mount Gower (right) and Mount Lidgbird (left) dominate the south end of the island. Photo courtesy of Julian Bielewicz.

The island is 375 miles (600 km) east of the continent of Australia and near the boundary between the Lord Howe Rise and the Tasman Basin. The Lord Howe Rise is made of continental crust that was rafted eastward as volcanism at a mid-ocean ridge formed new seafloor and opened the Tasman Basin. Seafloor spreading was active from 80 to 60 million years ago. The Lord Howe seamount chain, defined by coral-capped guyots, continues to the north for 600 miles (1000 km) and is probably the result of the Australia plate moving northward over a stationary hot spot. The Tasman Basin is greater than 4,000 m deep. The Lord Howe Rise is defined by the 2,000 m depth contour. Map from McDougall and others, 1981.

Lord Howe Island and Balls Pyramid cap a seamount that rises more than 5,900 feet (1,800 m) from the ocean floor. The seamount has an elliptical-shaped summit that trends to the north-northwest and is about 40 miles (65 km) long. The island is about 6 miles (10 km) long and about 1 mile (1.5 km) wide. A coral reef and lagoon are protected inside the crescent-shape of the island. Map from McDougall and others, 1981.

Mount Lidgbird (2,548 feet; 777 m) is made of caldera-filling, horizontal lava flows. The caldera wall passes through the northern flanks of the mount. Many of the flows have columnar jointing. The rocks record the rapid filling of a large caldera about 3 miles (5 km) in diameter. The caldera was filled with the lava flows about 6.4 million years ago. This was the most recent volcanic event at Lord Howe Island. Photo courtesy of Julian Bielewicz.

Mounts Gower is made of the same caldera-filling, horizontal lava flows that define Mount Lidgbird. The lavas are basaltic in composition. Flows range in thickness from a few meters to 100 feet (30 m). If volcanism associated with the hot spot that created the Lord Howe seamount resumes it will be about 250 miles (400 km) to the south. VolcanoWorld wishes to thank Julian Bielewicz for generously sharing his photographs.

Sources of Information:

McDougall, I., Embleton, B.J.J., and Stone, D.B., 1981, Origin and evolution of Lord Howe Island, Soutwest pacific Ocean: Journal of the Geological Society of Australia, v. 28, p. 155-176.

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