The Edinburgh Geologist
Issue no 28

The up-escalator of Papua New Guinea 

by Bill Baird

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Geologists working in Scotland are familiar with the raised beaches and wave-cut platforms around our coasts. These products of varying sea-levels and isostatic readjustment can be clearly seen in many areas including good examples around the Moray Firth and the coast of Argyll. At intervals of between 5 and 30 metres above the present sea-level these preserved landforms normally represent three main periods of formation, sometimes with several lesser features in between. 

Raised beaches and wave-cut platforms are therefore are features that we have either visited for ourselves, seen in pictures, or have read about. What can we make of the multiple raised beaches of Huon Peninsula, New Guinea? Not just three step-like terraces in the landscape, but a positive staircase of former shorelines Here, at least twenty raised marine terraces have been identified. These features were produced during periods when riding sea-levels temporarily overtook the continual uplift which occurs this part of New Guinea. The oldest of these terraces is dated at 300 000 years BP and stands at 150 metres above the present sea-level. 

A combination of circumstances has created this staircase of terraces on the coast of New Guinea: firstly, a consistently rising coastline due to the collision of the Australasian and Asian plates; and secondly, variations in sea-level during the Pleistocene ice age. Occasional periods of apparent equilibrium, when uplift and rising sea-level were matched, are marked by the formation of the coral reefs. These have been subsequently exposed as treads on the 'up escalator' as synchronisation was lost. 

Further reading

Chorlton, W and the Editors of Time-Life Books. Ice Ages. Time-Life Books. 

Chappell, J and Shackleton, N J. 1986. Oxygen isotopes and sea level. Nature, 324, 137-140.

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