An ancient buried landscape

An ancient buried landscape. The mountainous river-cut topography in the figure resembles that of the Ozark Plateau in the southwestern US. In fact, as Ross Hartley of Cambridge University and his colleagues have discovered, the craggy landscape lies off Scotland’s northern coast, buried beneath both the Atlantic Ocean and 2 km of rock. Hartley and his colleagues found the river-cut landscape in a three-dimensional seismic survey of Europe’s continental shelf. Being made of sedimentary rock, the landscape must have formed under water, but it was evidently once above sea level and exposed to the elements long enough for water to erode a network of valleys. How did the uplift take place? Water carves valley networks in more or less predictable patterns. When Hartley and his colleagues modeled the landscape’s erosion history, they found a surprise: The patterns could be explained only if the uplift took place over a total of 1 million years in three discrete steps, each about 200–400 m high. The uplift is consistent with the action of the putative Icelandic plume, a convective upwelling of hot material that extends from the lower mantle. When the plume reaches Earth’s crust, it spreads radially beneath the crust, exerting upward pressure. An unusually strong upwelling event could have lifted the now-buried landscape temporarily above sea level. (R. A. Hartley et al., Nat. Geosci. 4, 562, 2011 10.1038/ngeo1191 1752-0894.)