250m yr old volcanic explosion at Swansea Heads! What’s left?
250 million year old volcanic explosion at Swansea Heads! What’s left?
For 2020 Science Week, Hunter π in the Sci and Maitland Regional Museum are offering a quick look at coastal geomorphology, the possible effects of a destructive volcanic eruption, geology and understanding of earth processes at Swansea Heads over the past 250m years. A field trip is recommended.
This is a self-guided walk to explore clues left behind at Swansea Heads, NSW when a volcano exploded 250 million years ago.
Note on safety: Make sure you go when the tide is low and DO NOT GO IF THE SEAS ARE UP AS IT CAN BE VERY DANGEROUS. Allow about 2 hours on the rock platform. Be sun safe & take a hat and sunscreen. PLEASE wear a mask, stay home if you’re feeling unwell, observe 1.5m distancing from others, get tested if required to do so.
Swansea Heads Petrified Forest
Latitude -33°05’16.0”, Longitude 151°39’53.3”
Located in the Hunter Region of NSW, nearest town Swansea
Source: Field geology of New South Wales
Swansea Heads are located at the mouth of Lake Macquarie, the largest coastal lake in Australia. The Awabakal aboriginal people are the traditional owners of this land and the coastal platform provided plenty of resources for them. The southern headland at Swansea is called Reid’s Mistake after a collier captain in the 1800’s mistook the entrance to Lake Macquarie for that of the Hunter River at Newcastle.
Park your car in the car park at Reid’s Mistake Reserve. From there it is s short walk to the rock platform; time it so that you go at low tide.
The platform consists of tuff which overlays the Lower Pilot Seam. The headland has excellent exposures of the Boolaroo Formation including the Lower and Upper Pilot Seam and chert/ tuffs. The fossil tree stumps are common on the platform and appear to be situated in their original location with some fallen logs remained partly attached to stumps in a growth position.
The fallen trees have a mutual orientation leaning towards the west. This has led to the belief that the forest was laid flat by a volcanic eruption some 20km to the east that also covered the fallen trees with volcanic ash (tuff).
To see how this may have happened watch the US Geological Survey YouTube clip on the Mount St. Helens eruption in 1980 which shows the force of the shockwave which laid forests on their sides radiating out from the blast. Similar to Mount St Helens, at the Reid’s Mistake fossil site the hot pyroclastic material snapped off the trees and tilted the stumps towards the west aligning the trunks east west. Ash would then have settled on the tree stumps and flattened branches, and over time this ash has lithified into tuff. The remnant forest comprises ancient Glossopteris trees which have been fossilised for some 250 million years. There are many leaf fossils in fine laminated (indicates ash-fall) grey tuff scattered about the rock platform.
If you look at the headland behind the rock platform you will see two coal seams – the lower one, Reid’s Mistake Formation and the higher one Upper Pilot Seam. The Lower Pilot Seam is in the rock platform below your feet. Further south along the cliff, massive conglomerates with sandstone layers that belong to the Belmont Conglomerate Member.
Swansea Heads is located on at the southern entrance to Lake Macquarie. Reid’s Mistake is the southern headland of the lakes entrance. Access the area via the Pacific Highway at the large round-about at the southern end of Swansea. Here turn east into Bowman St, then turn left into Northcote Ave, then left into Hamilton St and then right into Lambton Parade and follow to the end and park at Reid’s Reserve carpark. Follow the path that leads to the small beach and rock platform.
Make sure you go when the tide is low.
Allow about 2 hours on the rock platform. Be sun safe & take a hat and sunscreen. DO NOT GO IF THE SEAS ARE UP AS IT CAN BE VERY DANGEROUS
You can download these instructions here.