Evaluation of morphometric proxies for uplift on sequences of coral reef terraces: A case study from Sumba Island (Indonesia)

Maëlle Nexer (1) , Christine Authemayou (2) , Taylor Schildgen (3) , Wahyoe S. Hantoro (4) , Stéphane Molliex (2) , Bernard Delcaillau (1) , Kevin Pedoja (1) , Laurent Husson (5) , Vincent Regard (6)

1 M2C - Morphodynamique Continentale et Côtière
2 LDO - Domaines Océaniques
3 University of Potsdam = Universität Potsdam
4 Research Center for Geotechnology
5 ISTerre - Institut des Sciences de la Terre
6 GET - Géosciences Environnement Toulouse

Sequences of coral reef terraces characterized by staircase morphologies and a homogeneous lithology make them appropriate to isolate the influence of uplift on drainage morphology. Along the northern coast of Sumba Island, Indonesia, we investigated the correlations between landscape morphology and uplift rates, which range from 0.02 to 0.6 mm·yr− 1. We studied eight morphometric indices at two scales: whole island (~ 11,000 km2) and within sequences of reefal terraces (~ 3000 km2). At the latter scale, we extracted morphometric indices for 15 individual catchments draining mostly the reefal terraces and for 30 areas undergoing specific ranges of uplift rates draining only the reefal terraces. Indices extracted from digital elevation models include residual relief, incision, stream gradient indices (SL and ksn), the hypsometric integral, drainage area, mean relief, and the shape factor. We find that SL, the hypsometric integral, mean relief and the shape factor of catchments positively correlate with uplift rates, whereas incision, residual relief, and ksn do not. More precisely, we find that only the areas that are uplifting at a rate faster than 0.3 mm·yr− 1 can yield the extreme values for these indices, implying that these extreme values are indicative of fast uplifting areas. However, the relationship is not bivalent because any uplift rate can be associated with low values of the same indices. For all indices, the transient conditions of the drainage influence the correlation with Pleistocene mean uplift rates, illustrating the necessity to extract morphometric indices with an appropriate choice of catchment scale. This type of analysis helps to identify the morphometric indices that are most useful for tectonic analysis in areas of unknown uplift, allowing for easy identification of short spatial variations of uplift rate and detection of areas with relatively fast uplift rates in unstudied coastal zones.

Mots clés: Pleistocene; Sumba Island; Indonesia; Drainage morphometry; Coral reef terraces; Uplift

Domaines: Tectonique

Maëlle Nexer, Christine Authemayou, Taylor Schildgen, Wahyoe S. Hantoro, Stéphane Molliex, et al.. Evaluation of morphometric proxies for uplift on sequences of coral reef terraces: A case study from Sumba Island (Indonesia). Geomorphology, 2015, 241, pp.145-159. ⟨10.1016/j.geomorph.2015.03.036⟩. ⟨insu-01164282⟩