Tag Archives: Bonnet Hill

Geological and Social History of our Alum Cliffs

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Patricia Roberts-Thompson (http://taroona.tas.au/assets/document/1354363720-a_walk_along_alum_cliffs.pdf) indicates that the first recorded reference to the Alum Cliffs was in 1847.  She explains that these rocks, Permian mudstone (250 million years old, contain iron pyrites and, as the rock weathers, the pyrite oxidises and produces sulphuric acid which reacts with the limey clay to produce alum. Roberts-Thompson could find no evidence that the alum has been extracted from our cliffs for commercial purposes.

Simon Stephen’s research (http://taroona.tas.au/assets/document/1352547986-geology_reduced.pdf) is in sync with that of Patricia Roberts-Thompson  when he says the mudstone on the Alum Cliffs contains much sulphur so that when struck a strong smell is emitted. “Much of the sulphur manifests itself as a white encrustation on thee sheltered areas of the cliffs. It has a distinct bitter taste…”  (Trust me – I won’t be taking a bite or licking it). Stephen’s article is exceptionally interesting not the least because it pin points a geological fault line which is near Crayfish Point (where I have already walked) and which extends out through the end of Hinsby Beach and then under the water along the Alum Cliffs.  I don’t know if any seismological activity has occurred in my life time there nor whether any is expected. I’d rather nothing happened during my forthcoming Stage 12 walk along the Alum Cliffs.

The Kingborough Council distributes a brochure with the following information: “The route followed by today’s Alum Cliffs Track has long been a coastal path used by local people. In 1988 it was formally developed as part of Australia’s Bicentennial celebrations. In more recent years, Council has upgraded the southern section of the track, which climbs from Tyndall Beach through coastal blue gum forest with tall silver banksias. The track then winds up through silver peppermint bushland, dips into a glorious fern filled gully, before rising again onto headlands for commanding views over Storm Bay and the Derwent Estuary. A new start to the track without steps has now been constructed above Tyndall Beach to make the track accessible to more users. The Alum Cliffs are so named because alum – a compound used in dyeing, tanning and medicinal products – is found in the cliffs.”

It is a shame that all instructions to reach and walk the Alum Cliffs use Kingston Beach in the south as the base to walk north and then return. Websites provide information about multiple entrances along the route at Tyndall Rd, Harpers Rd, Taronga Rd.  Apparently a Metro bus stop is located 100m south of the intersection of Taronga Rd and Channel Highway. I wonder how many people have walked the Alum Cliffs Track from the northern end and, if not, like me would like to read advice about how to tackle the cliffs departing from Hinsby Beach.

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It may be that, on Stage 12, I will start out at the end of the Hinsby Beach and then be forced to retrace my steps, return to the Channel Highway and walk up the winding fairly narrow Highway with no pedestrian walkway until I reach the Brickfields Track. From http://www.greaterhobarttrails.com.au/track/brickfields-track I understand that “the Brickfields Track links between Taronga Rd (adjacent to the Channel Highway) in Bonnet Hill and links to the Alum Cliffs Track. The route of the Brickfields Track takes you through the historic remains of the brick-making area; part of the nearby and short lived 1840’s convict probation station. The track is a mix of narrow bush track and timber boardwalk with some steps along the route.”

Stage 2 on 4/9/2014 Mitchell’s Beach Email 4 of 14

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The roadway above Opossum Bay beach being narrow and without public footpaths meant it was important not to day dream and for me to be vigilant for the occasional car.  But Opossum Bay is a relaxed seaside village and even cars seem to move sedately.

I continued walking on the road from Opossum Bay beach until I reached a 50Km hour sign for cars, then I moved left off the road onto a well-trodden narrow track through a clutch of Casuarina trees and walked down to the next beach – Mitchell’s Beach. When I checked my watch, only 20 minutes had passed since I had left the bus. Yet already my head was filled with ideas and new information, and my heart was open with joy. The pleasure of walking in clean clear environments cannot be underestimated.

The winding track from the road finished on the sandstone rocks. After an easy few movements and a short distance, I walked onto the sand of Mitchell’s Beach. As I padded along the beach, a gentle breeze whispered across my face while the water lapped quietly onto the sandy shore. Silver gulls wandered around. Opened mussel and oyster shells strewn along the beach, were blanching in the sunlight. I marvelled at the various seaweeds thrown up at high tide, at the decaying ribbons of sea grass and at the fish eggs collapsed like bizarre multi-shaped condoms. The air was rich with the sweet and salty smell of dying seaplants. The water a soft greeny grey. Blissful.

When I come across a few bright orange starfish on the edge of the tide, I cartwheeled them into the dry sand at the upper edges of the beach. I was simply doing my tiny bit to reduce the infestation of these seastars (http://www.abc.net.au/science/slab/starfish/) as devastating invaders of our local marine environment.

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From Mitchell’s Beach I looked directly across the Derwent River and could see the suburbs of Kingston and Taroona with the Alum Cliffs below Bonnet Hill between them. Strikingly, Taroona’s Shot Tower stood tall.  Stunning.

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A pair of footprints impressed in the sand let me know that someone had walked the beach earlier.

Mitchell’s Beach was edged with three to four metre high dunes with tussocky grass on top, which were gradually crumbling into the beach. Demarcations between dirt and sand strata were clearly visible. Towards the northern end of the beach, small seas of water smoothed grey stones provided a separation layer between the beach and the dunes.

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A lone Dominican gull with his pure white tail, pale grey legs and small yellow bill flew off leaving me in charge of his beach.

I reached the end of Mitchell’s beach 40 minutes or so after setting off from the Opossum Bay shop. Again a rocky headland stopped me continuing but I couldn’t see a defined track up the hill onto the land at the top.  Clearly people had found a way judging from a mishmash of bits of tracks.  I chose the least steep section and was surprised when after my first steps up I slid back down. The previous day’s rain had kept the ground lush and damp, and it was clear that the soil included slippery clay. By a more careful choice of foot placements, I eventually reached the top.

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