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Ball's Pyramid

VOLCANIC GEOLOGY

Lord Howe Island and Ball's Pyramid are the last remnants of two volcanic seamounts that formed around 7 million years ago.

Geologists believe that there were two main volcanic episodes in the formation of Lord Howe Island. Most of the volcanic activity took place some 6.9 million years ago, and comprised several volcanic vents, ultimately producing a large shield volcano about 30 km in diameter. It is thought that the volcano’s maximum height above sea level was about 1,000 metres.

Around 6.3 million years ago the area around the main vent collapsed and left a huge oval-shaped pit or caldera, perhaps five kilometres long, two kilometres wide, and 900 metres deep. At this time further volcanic material pushed up from beneath the earth’s crust to infill the caldera in a series of horizontal lava flows, varying from one to thirty metres in thickness. In this second period of volcanic activity, the basalt rocks were harder and more erosion resistant, standing today as magnificent ramparts of the southern mountains which still rise to 875 metres above sea level.

Remnants of the volcano

Vertical dykes in cliffs

Lava layers

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