TASMANIAN MOUNTAINS: Matthew Flinders & the Coastal Landforms of SE Australia

The Norfolk expedition was to prove that Tasmania was an island through its anticlockwise circumnavigation. The Great Western Tiers and other peaks of this escarpment were viewed while exploring the north coast. 'Stupendous' peaks were seen from the west coast. Mt Wellington, near present-day Hobart, was climbed by George Bass, while Flinders climbed Mt Direction. Ben Lomond, reported earlier by Dutch explorer Tasman, was viewed from the east coast, while the Norfolk was sailing northwards on the return voyage to Sydney. Locations on this page will be discussed in the sequence visited by Flinders and Bass.
Northern Escarpment (Tiers) Tasmania is quite diverse in terms of rock types and landforms. Along the northern part of the state, much of the Central Plateau is edged by a steep escarpment that parallels the coastline. This serves to isolate the highland areas from the coast, and to funnel transportation along the coastal plain. Parts of Tasmania are of Tertiary basalt, including a patch below the Tiers. These areas can be quite productive. However, on the plateau, harsh climate and poor soil development prohibit most agricultural activities. Large areas are still close to their natural state.	Photo 1: Northern Escarpment (Tiers), Tasmania
Along the northern coast of Van Dieman's Land (Tasmania) Flinders and Bass sailed the Norfolk westwards, into the unknown. They landed on islands and coastal points, but did not explore far inland (although they expended considerable effort and time exploring around the Tamar, site of present-day Launceston). While sailing, and from coastal observation points, they could gain glimpses of the north-facing escarpment and the interior highlands. '... the blue tops of the inland mountains show over the coast range here and there.' *[ Matthew Flinders in Norfolk* Narrative, p.41 ] 'Parent mountains showing their blue heads just over them ... the mass inland ... which the blue distant mountains are the apex ... the land is uncommonly high and irregular being in the nearest part a kind of table land and afterwards intersected into uncouth shapes and peaks. From the brilliancy of some parts, on the appearance of the sun after rain, I judged them to consist of granite, like the mountains of Furneaux Islands.' [ Matthew Flinders in Norfolk Narrative, p.33 ]**
Cradle Mtn, north-central plateau Cradle Mountain (and many other central peaks and east coastal cliffs of Tasmania) is composed of dolerite, an igneous rock that was injected into a sill beneath a sedimentary capping (relatively near the surface) during the Jurassic period. Subsequently, the capping was removed to expose the resistant dolerite below. Jurassic dolerite is found in many parts of Tasmania. Its formation is probably related to the crustal splitting (i.e. the rifting process) at the start of the breakup of the super-continent Gondwana when Australia began to move away from Antarctica and a sea formed between them.	Photo 2: Cradle Mountain and plateau from summit (Little Horn on right)
Much later, during the Pleistocene Epoch (Ice Age), parts of the Tasmanian Highlands were covered by glaciers. Ice caps occupied the higher areas while valley glaciers moved downwards, along river valleys, eroding landform features, many of which still remain today. A still larger area of the state was affected by freeze-thaw (periglacial) conditions. At the end of the Ice Age the glaciers retreated and then disappeared, leaving behind depositional materials known as moraines. Moraines blocked and dammed some stream, giving a number of the glacial lakes visible today. While it is possible to also study the direct action of glaciers in the Snowy Mountains of NSW, the Tasmanian Highlands offer a larger area and more diverse range of glacial features in Australia from the most recent glacial period.
The well known view of Cradle Mountain, with Dove Lake in the foreground, can be regarded as a Tasmanian icon. On postcards, calendars, brochures, and other items, the beauty of this area is 'exported' around the world. Yet it is important that the area be protected, rather than simply being seen as an 'economic opportunity'. Thankfully, this is so. Here, and in many other parts of Tasmania, protection of landscape, ecology, cultural heritage, wilderness value and high quality visitor experience, is afforded through management by the Parks and Wildlife Service. Much of the charm and beauty of the Tasmanian Highlands comes from a combination of their rugged nature and unique plant life. Photos 3&4 (right) illustrates rock types and plant communities. The peaks are resistant 'spires' of Jurassic dolerite, lying over older rocks of Triassic-Permian sediments. Underlying this is ancient basement rock, much of which in Tasmania is metamorphosed. Thus, in a vertical 'slice' of terrain, it is possible to view the three main types of rock, igneous, sedimentary, and metamorphic. The properties of the rock (including resistance to weathering and soil-forming minerals can greatly influence the resulting landforms, ecosystems, ecology, landuse by indigenous and European inhabitants, and the 'general appearance' of the land.	Photo 3 Cradle Mountain - Dove Lake Photo 4: Cradle Mountain - Dove Lake Major geological formations (red), natural features (yellow)
Vegetation in alpine regions, such as the Tasmanian Highlands, has adapted to the extreme conditions present; long, cold and windy winters, frequent frosts and periodic snowfalls, poor drainage and low soil nutrient levels, even trampling by people careless enough to leave the walking track. Life here is fragile for plants and animals; a deterioration of present conditions could lead to stress and possibly species loss.
Western Tasmania The prominent peak in the distance, Frenchmans Cap (1400m), composed of ancient quartzite, was 'sharpened' by ice erosion in the most recent glacial period. A glacier carved a series of bowl-shaped depressions (or cirques) which eventually joined up, on the right hand side of the mountain. Perhaps the outline below, taken from Flinders' description of Port Davey, could also apply to the view (right), from Macquarie Harbour (somewhat north of Port Davey). Both these harbours are drowned valleys, legacies of past lower sea levels, when rivers carved deeper courses, which subsequently became 'flooded' when the sea level rose after the glacial period.	Photo 5: Frenchmans Cap and other highland peaks from Macquarie Harbour (west coast)
View of the inland mountains from the mouth of Port Davey, SW Tasmania 'The mountains which presented themselves to our view in this situation, both close to the shore and inland, were amongst the most stupendous works of nature I ever beheld, and at the same time are the most dismal and barren that can be imagined; The eye ranges over these peaks and variously formed lumps of adamantine rock with astonishment and horror, had the thermometer been 30° or 40° [Farenheit] lower, and our distance from the land been somewhat greater, the white streaks and patches of bare rock might have been taken for snow ... ' - Matthew Flinders in Norfolk Narrative
Ben Lomond Field evidence indicates that a small ice cap covered the Ben Lomond plateau (photo, right), above 1350m during the peak of the most recent glacial period. At this time snow built up, forming glacial ice. Apart from the major ice cap on the central plateau, a number of other smaller ice sheets accumulated over Tasmania. Ice sheets move steadily under the influence of gravity, grinding away and smoothing out peaks and bumps, and deepening low areas, forming hollows that may later fill with water, giving rise to lakes. Prior to and after this time periglacial processes also brought about landform changes. These processes result from the freeze-thaw of water that occurs as temperatures frequently rise and fall below 0°C. Ice expansion can assist rock breakdown. These processes continue today in many upland areas for at least 5 months of the year (including Ben Lomond and Mt Wellington).	Photo 6: Summit plateau, Ben Lomond
Periglaciation involves two important processes; frost shattering of rocks and mass movement of rock fragments in block streams. It is possible that periglacial processes have brought about greater landform change than direct glaciation, perhaps in part as it has operated over a wider area for a longer time.
Ben Lomond (1575m) is visible from a large distance. Close-up, vertical cooling columns (or 'organ pipes') of dolerite can be seen, suggesting that cooling of magma did not take place on the surface nor deep underground; rather, as an intrusion into a sill. This is also believed to be the origin of the other dolerite peaks of the Tasmanian Highlands.	Photo 7: Ben Lomond, northeastern Tas
Ben Lomond appears on Flinders' chart. It had been sighted previously by Dutch explorer, Tasman. ' ... ridge of stony hills ... peak like volcano ... high rugged mountains ... very high rocky mountains ... Benlomen Flat topped ... ' - Extract from Flinders' chart	Ben Lomond chart Extract from Flinders' chart (Ben Lomond)