The juvenescence of the Walvis Ridge – evidence for recent submarine volcanism from hydro-acoustic data in the vicinity of Tristan da Cunha

Wolfram.Geissler [ at ]


The Walvis Ridge-Rio Grande Rise System is the only seamount chain in the Atlantic that is known being continuously active since the Cretaceous (130 Ma) and one of very few worldwide, that links an active hotspot (Tristan-Gough) with a continental flood basalt province (the Paraná-Etendeka province in South America and Africa). Previous work has documented age-progressive volcanism along at least parts of the Walvis Ridge and several initiatives acquired new geophysical and petrological data from seamounts of the Walvis Ridge and its southerly neighbours over the last decade. The youngest stretch of the Walvis Ridge, the islands of Tristan da Cunha, was the focus of the ISOLDE project within the DFG priority program SPP1375 „South Atlantic Margin Processes and Links with onshore Evolution (SAMPLE)”. Temporary seismological and magneto-telluric measurements were carried out to characterize the upper mantle in the search for evidence of a mantle plume. Two expeditions with R/V MARIA S. MERIAN headed towards this remote area to install and dismantle ocean-bottom stations in 2012 and 2013, respectively. Hydroacoustic data were collected along the tracks and around the islands, allowing a first detailed bathymetric insight to the area, underpinned by backscatter and sediment echo sounder observations. One unexpected outcome was the discovery of a new submarine volcano, Isolde Seamount, at the eastern flanks of Nightingale Island. Isolde lies very close to the assumed site of a submarine eruption in 2004, known only from floating pumice and seismicity. Further submarine volcanic centres could be mapped around the islands. Of interest are two volcanic fields, each about 20 x 40 km across, to the NW of Inaccessible Island, where small monogenetic volcanic cones and young lava flows were mapped. Young volcanic activity seems to extend up to 250 km westwards from the Tristan group to about 14.8 W, where we mapped a small volcanic cone on top of old abyssal hills only 130 km east of the Mid-Atlantic Ridge. Further westward, normal seafloor fabric, with clearly defined abyssal hills, dominates the seafloor. Scattered volcanic activity is visible along and in close vicinity to the Tristan da Cunha Fracture Zone. The intraplate volcanic fields as well as the scattered probably monogenetic submarine volcanoes could indicate that the Tristan mantle plume (or at least part of it) currently sits to the west/southwest of Tristan da Cunha.

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Ge­o­B­re­men 2017, 24 Sep 2017 - 29 Sep 2017, Bremen.
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Geissler, W. , Wintersteller, P. , Strack, A. , Kammann, J. , Jegen, M. , Maia, M. and Jokat, W. (2017): The juvenescence of the Walvis Ridge – evidence for recent submarine volcanism from hydro-acoustic data in the vicinity of Tristan da Cunha , Ge­o­B­re­men 2017, Bremen, 24 September 2017 - 29 September 2017 .

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