Landforms of aeolian, tectonic and marine origin in the Bauer Bay-Sandy Bay region of subantarctic Macquarie Island

Adamson, DA; Selkirk, PM; Colhoun, EA

doi:10.26749/rstpp.122.1.65

Cited by 19 publications

(9 citation statements)

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“…There are no data or observations on other processes of coastal erosion onMacquarie Island, but it is worthnoting that the minimum computed rate for kelp-assisted bioerosion (0.1 mm yr-l) is far lower than estimated rates of Macquarie Island uplift of 1.5-5.0 mm y r ' (Selkirk et al 1990). The role that we suggest for kelp-assisted erosion is therefore not inconsistent with the model of shore development proposed by Adamson et al (1988) in which marine cut terraces were eroded during a period ofrising sea levels between 16000 and 8000yearsag0, andsincethattime havebeenraisedabove sea level by uplift, forming the present narrow coastal plain (particularly on the more rapidly eroded west coast).…”

Section: Quantitative Estimates Of Erosion By Kelp-pluckingsupporting

confidence: 53%

Kelp-plucking: coastal erosion facilitated by bull-kelp Durvillaea antarctica at subantarctic Macquarie Island

Smith

Bayliss‐Smith

1998

Antartic science

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Erosion of bedrock from lower intertidal reefs by waves acting on attached plants of bull-kelp (Durvillaea antarctica) was investigated over one year at Macquarie Island, Southern Ocean. At a site on the more sheltered east coast, such erosion occurred during four separate storms, each casting up 834–1078 large kelp plants km−1 of coast, of which 30–45% were still attached to jagged, freshly quarried bedrock fragments over 2.5 cm long. The largest fragment weighed was 74.6 kg; rounded cobbles and boulders attached to kelp plants and weighing up to 102.2 kg (and probably more than 160 kg) were also cast up on beaches. 19–21% of the standing crop of large kelp plants was removed by storms during the year of observation. Break points for 10 kelp stipes were found to be at least 90–161 kg. Total annual erosion by kelp-plucking is at least 1.56 tonnes of rock km−1 of coast. However, in terms of erosion this computes to only 0.1 mm yr−1, far below the rate of uplift of the island.

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Section: Quantitative Estimates Of Erosion By Kelp-pluckingsupporting

confidence: 53%

Kelp-plucking: coastal erosion facilitated by bull-kelp Durvillaea antarctica at subantarctic Macquarie Island

Smith

Bayliss‐Smith

1998

Antartic science

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“…They have also been described from subantarctic and glacial environments (e.g. Adamson et al, 1988).…”

Section: Blowouts: Definition Types and Spatiotemporal Variabilitymentioning

confidence: 99%

Flow dynamics and geomorphology of a trough blowout

Hesp¹,

Hyde²

1996

Sedimentology

104

121

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The dynamics and geomorphological development of a trough blowout located at Fiona Beach in the Myall Lakes National Park in NSW, Australia, are examined. Wind speeds, velocities and flow structure were measured utilizing an array of miniature Rimco cup anemometers, Gill bivane and UVW instruments, and wind vanes. Flow measurements indicate that when the wind approaches the trough blowout parallel to the throat orientation, jets occur both in the deflation basin and along the erosional walls, relative flow deceleration and expansion occurs up the depositional lobe, jets are formed over the depositional lobe crest accompanied by downwind flow separation on the leeward side of the lobe, and flow separation and the formation of corkscrew vortices occur over the crests of the erosional walls. Maximum erosion and transport occurs up the deflation basin and onto the depositional lobe. Trough blowout morphologies are explained as a function of these flow patterns. When the wind approaches the blowout obliquely, the flow is steered considerably within the blowout, and the degree and complexity of topographic steering is dependent on the blowout topography. The flow is usually extremely turbulent and large corkscrew vortices are common. The local topography of a blowout can be very important in determining overall sand transport and blowout evolutionary conditions and paths. Estimates of potential sand transport within the blowout may be up to two orders of magnitude lower than actual rates if remotely sensed wind data are used.

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“…Macquarie Island is a steep-sided mountainous plateau 200-400+ m a.s.l., rising from a gently sloping platform cut during marine transgressions following the periods of world wide low sea level (Adamson et al 1988). This platform extends offshore on all sides of the island to a depth of at least 100 m: to the west it is 2-4 km wide, on the east it is narrower, while to the north and south, it extends at least 30 km.…”

Section: Island and Ridge Morphologymentioning

confidence: 99%

“…The assumption is also made that the beaches preserved on the island represent the major transgressions of the middle and late Quaternary, and that none are missing, with the partially exposed marine terrace close to present sea level representing the postglacial transgression between about 18 and 6 ka (Adamson et at. 1988, Selkirk, P.M. et al 1990a).…”

Section: Cross-matching the Timing Of High Global Sea Levels With Thementioning

confidence: 99%

Pleistocene uplift and palaeoenvironments of Macquarie Island: evidence from palaeobeaches and sedimentary deposits

Adamson¹,

Selkirk²,

Price³

et al. 1996

PPRST

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Macquarie Island (54°30'5, l 59°00'E) is an emergent part of the Macquarie Ridge Complex composed of ocean-floor rocks of Miocene age now 4000 m above the ocean floor. A number oflandforms, including palaeobeaches now above sea level (a.s.l.)on Macquarie Island, were formed by marine erosion during uplift of the island. During the last Pleistocene period oflow sea level (c. 20 ka) the island was three times larger than now. Thermoluminescence (TL) dating of two palaeobeaches indicates Pleistocene ages: 172 ± 40 ka for one at 100 m a.s.l. and 340 ± 80 ka for another at 263 m a.s.l. Matching the altitude sequence of palaeobeaches on Macquarie Island with the pattern of peaks in world sea level determined from deep sea cores allows an independent estimate of beach ages. Comparison of the altitude and sea level sequences most plausibly places the 100 m palaeobeach in Oxygen Isotope Stage Se (130-125 ka) and the 263 m palaeobeach in Stage 9 (340-330 ka), matching reasonably with the TL dates. Other palaeobeaches at about 50 m and 170-190 m a.s.l. then correlate with high sea levels. We calculate an average rate of uplift for the island of0.8 mma-1 • At this rate, 4000 m of Macquarie Ridge uplift would have taken about five million years and the top of the island may fi rst have emerged some 700 to 600 ka. During the six Pleistocene glacial interglacial cycles since then, there has been periglacial rather than glacial activity on cold uplands, but conditions suitable for vegetation of the present type persisted close to sea level.

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Landforms of aeolian, tectonic and marine origin in the Bauer Bay-Sandy Bay region of subantarctic Macquarie Island

Cited by 19 publications

References 0 publications

Kelp-plucking: coastal erosion facilitated by bull-kelp Durvillaea antarctica at subantarctic Macquarie Island

Kelp-plucking: coastal erosion facilitated by bull-kelp Durvillaea antarctica at subantarctic Macquarie Island

Flow dynamics and geomorphology of a trough blowout

Pleistocene uplift and palaeoenvironments of Macquarie Island: evidence from palaeobeaches and sedimentary deposits

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