Underwater volcanic craters and reefs found off Wollongong coast

DISCOVERING: OEH marine scientist Dr Tim Ingleton (left) on board research vessel RV Bombora mapping seafloor off Wollongong, from Bellambi Point to Red Point (Five Islands). Picture: Office of Environment and Heritage.
DISCOVERING: OEH marine scientist Dr Tim Ingleton (left) on board research vessel RV Bombora mapping seafloor off Wollongong, from Bellambi Point to Red Point (Five Islands). Picture: Office of Environment and Heritage.

Anglers in Wollongong have always suspected.

But it was University of Wollongong marine scientists “who officially discovered the rocky reef off the Wollongong coast”.

NSW Office of Environment and Heritage then jumped on board and discovered large areas of reef, ancient volcanic vents and relict rivers formed thousands of years ago on the sea floor off the Illawarra coast. 

UOW marine science PhD candidate Allison Broad said no-one was prepared for how much reef was discovered following further OEH seabed mapping.

“Almost 60 per cent of this region is rocky reef habitat and this extends to more than five kilometres offshore in water depths to at least 60 metres,” she said.

“This is highly significant because temperate rocky reefs house significantly more biodiversity than soft sediment environments like sand and mud.”

These intriguing crater features may have been formed by ancient volcanic activity in the area.

OEH marine scientist Dr Tim Ingleton

Ms Broad said UOW researchers were investigating large commercial ships anchoring on seafloor offshore Wollongong when presented with anecdotal information that a reef existed.

She said once confirmed this peaked the interest of OEH, who then made the Wollongong region a priority of their seafloor mapping project.

OEH marine scientist, Dr Tim Ingleton said the mapping is part of an ongoing effort to create a high-resolution digital map of the NSW seafloor (SeaBed NSW), to better understand the distributions of reef and soft sediment environments.

OEH research vessel RV Bombora.

OEH research vessel RV Bombora.

OEH scientists have systematically scanned the first section of seafloor off Wollongong, from Bellambi Point to Red Point (Five Islands), using sonar and video systems mounted on research vessel RV Bombora.

“We discovered evidence of ancient river channels that flowed thousands of years ago when sea level was lower and the coastline was located far offshore, which was confirmed by sediment samples containing smooth and round pebbles typical of fluvial environments,” he said.

“We also noticed a few strange round patterns that looked like ‘crop circles’ on the sea floor.

“These intriguing crater features may have been formed by ancient volcanic activity in the area.

Sponge garden at Five Islands.

Sponge garden at Five Islands.

“Volcanic features called Diatremes form as magma rises through a crack in the Earth's crust and meets ground water. Super-heated water vapor and volcanic gases rapidly expand, causing explosions that leave behind a shallow crater.”

OEH scientists have mapped as much as 15 per cent of the state’s coastal waters since 2005.

Dr Ingleton said the SeaBed NSW program will expand on that systematically, using RV Bombora and state-of-the-art equipment to collect high-resolution data on the depth and composition of the seabed across targeted sections of the NSW coast.

“The data will be made available to researchers, councils and the public,’’ he said.