Lithospheric flexure and uplifted atolls

Abstract

Contrary to the expectation that islands should monotonicalIy sink as the aging sea floor thermally contracts, some atolls that were formerly at sea level are now elevated as much as 70 m. A eustatic sea level high cannot explain the magnitude of the larger uplifts or the simultaneous occurrence of elevated and sea level atolls. The observation that recently active volcanoes are found near these raised atolls suggests that they have been tectonically uplifted by the loading effect of the volcanoes. By modeling the oceanic lithosphere as an elastic plate overlying a fluid asthenosphere we can both explain the varying amounts of elevation and bracket the effective flexural rigidity of the oceanic lithosphere between 1.7 and 2.5 ×1022 N m.

Late Quaternary sea-level and tectonic changes in northeast Fiji

“…Similar situations are known to have occurred in other Paci¢c Island groups (McNutt and Menard, 1978;Dickinson, 1998;Dickinson and Green, 1998), although are unlikely to be occurring at present in the study area because £exural compensation is generally complete within 100 000 years of the imposition of a volcanic load. A characteristic moat-and-arch bathymetry is not readily observable in the available bathymetry (see Fig.…”

Coastal evolution on volcanic oceanic islands: A complex interplay between volcanism, erosion, sedimentation, sea-level change and biogenic production

“…For example, islands located on plates that are stationary with respect to their melting source, such as the Cape Verdes, are prone to long term uplift movements (up to 400-450 m at 0.4 mm/yr) possibly driven by basal intrusions and by hotspot swell growth Ramalho et al, 2010a,b,c;Ramalho, 2011). Cumulative far field effects of surface loading by other islands in the vicinity may also cause uplift, as is inferred for O'ahu (0.02-0.07 mm/yr), Moloka'i (0.04-0.19 mm/yr), and Lana'i (0.15-0.29 mm/yr) in Hawai'i, and for other Pacific uplifted atolls in the Cook-Society island region (McNutt and Menard, 1978;Grigg and Jones, 1997;Rubin et al, 2000;McMurtry et al, 2010). Likewise, islands located near active plate margins may experience uplift as a result of dynamic topography (near divergent plate margins) or plate flexure/buckling associated with outer trench rise (near convergent plate margins) (Karig et al, 1976;Melosh, 1978).…”

“…In a similar fashion, accretion rates may differ according to environmental and oceanographic conditions and will have a profound effect on reef morphology. Local uplift -whose origins are still poorly understood or are the focus of hot debate (see Scott and Rotondo, 1983;McNutt and Menard, 1978;McMurtry et al, 2010;Ramalho et al, 2010b) -may further contribute to the variability in reef morphology. It is now perceived that the diversity of modern reef morphology essentially arises from the combined effects of island subsidence (or sometimes uplift), coral accretion rates, and Pleistocene glacioeustatic cycles (Woodroffe et al, 1999;Toomey et al, 2013).…”

Thermo-hydro-mechanical processes in fractured rock formations during a glacial advance

“…Figure 12 shows the vertical displacement or deflection in the rock mass with fracture zones at time 5900 years. The displacement is negative under the glacier, which is indicative of the mechanical compression of the rock, and positive outside the glacier, which is indicative of the conventional heave associated with glacial loading (Walcott, 1970(Walcott, , 1976McNutt and Menard, 1978;Selvadurai, 1979Selvadurai, , 2009bSelvadurai, , 2012 Selvadurai and Nguyen, 1995). The maximum negative displacement (−0.076 m) is near the front of the glacier at its initial position.…”

“…Peltier, 2004) are not accounted for in the current modelling, although it is an important consideration in a more complete investigation of the glacial loading problem. The crustal movements can continue for several millennia due to creep and viscoelastic effects (Walcott, 1970(Walcott, , 1976McNutt and Menard, 1978;Selvadurai, 1979) and a glaciation episode needs to be considered in the context of GIA that needs to be accurately estimated to provide a reference state.…”