Thursday 26 March, 2026

Five and six sided columns in cross-section created by sea erosion

The wave platform showing the area of columnar basalt

Some of the columns are finally succumbing to the erosive power of the ocean

Skirting the basalt columns along the cliff line

Outcrop of silcrete on the cliffs above the basalt platform

Ian disturbing a termite mound for our biology lesson

Everyone was counting the sides of the eroded columns

Julie “rock scrambling” along the narrow coastline

Photos and walk report courtesy of Co-Walk Leader Rob

Five walkers including an adventurous visitor explored the basalt outcrops along the shore platform and cliffs at Black Head, Congo. The location Black Head is a local name and appears to be related to the very dark basalt rocks exposed at this point in the Eurobodalla NP. A bit of background – Geologists believe a volcanic fissure erupted in the Bodalla area approximately 29 million years ago. A series of lava flows extended north and east. Much of the basalt had been eroded away and today we see outcrops in the Tuross and Coila areas with the northern most extent being at Broulee Headland, before disappearing out to sea. Our walk explored the basalt outcrops along the coastline at Congo. The shore platform at this point is very narrow so any walk must be done at low tide. The cliffs consist of basalt columns that have been breaking off and are now a jumble of boulders we had to scramble over to reach the narrow wave cut platform. Once we reached the platform we could see the cross-section of old eroded columns. Each column is a 5 or 6 sided feature showing that, as the basalt cooled, it contracted into the most efficient shape – a pentagon or hexagon.

Continuing south along the beach we joined the Dreaming Track and headed inland into the open forest terrain. This area was almost completely stripped of vegetation over 150 years ago by early settlers for grazing activities. The sandy soils in this forest area did not prove productive and the forest was allowed to regrow. Ian Barnes, our resident forester, pointed out a number of original trees that predate white settlement but most of the trees are very young. We found a termite mound that Ian prodded with a stick that brought out what he called ‘defence ants’ – small brown bodies with black heads. It’s always an education lesson when Ian comes on a walk.

Finally, we ended the walk on the cliffs above the basalt columns where we saw an outcrop of silcrete. This is silica (like quartz) but formed when dissolved silica comes out of groundwater to form a solid layer. This silica was a source of rock used by First Nations people to create tools.

With the natural history lessons complete we headed back to the Congo Campground for lunch, finishing just before the rain started. All in all a great days outing.