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That the plume tail arose in pulses of varying temperature was suggested by White et al. (1995) following Vogt (1971), from consideration of the strength of the V‐shaped ridges of the ocean floor south of Iceland. These ridges, signifying thickened oceanic crust, straddle the mid‐ocean ridge on either side of Iceland. The thickenings are held to be due to fluctuating temperatures as unusually hot pulses in the underlying asthenospheric mantle radiate away from Iceland (Poore et al. 2009, 2011). These authors propose that the hot pulses, with a temperature some 25 °C hotter than that of the back‐ground plume temperature, arise intermittently through a plume conduit (with a radius of ~150 km) under Iceland. The upwelling rate in the conduit is estimated at 27 cm/year with the rate of radial spreading beneath the lithosphere being ~40 cm/year (Poore et al. 2011). Since the varying temperature of the out‐flowing mantle causes elevation or subsidence of the overlying crust (White et al. 1995; Wright and Miller 1996; White and Lovell 1997), it has important stratigraphical implications; hot pulses are responsible for sea‐floor elevation, leading in turn to increased erosion. Consequently, the stratigraphic sequences in the sedimentary basins retain records of intermittent uplifts (White and Lovell 1997; Hartley et al. 2011).

Figure 13 Lava fountaining along a fissure (Krafla volcano) northern Iceland 1980, during an episode of extension and rift opening.

Source: Photo by Halldór Ólafsson.

At times during the Cenozoic parts of the European continental shelf were so markedly elevated as to be raised above sea‐level and river systems were established. The reconstructed history of one of these ancient landscapes, dating from the Palaeocene–Eocene thermal maximum, has shown that it was lifted above sea‐level in three distinct steps, each of 200–400 m. After about one million years of sub‐aerial erosion, it sank again beneath the sea. Thus the asthenospheric mantle radiating from the Iceland plume was inferred not to have had a constant temperature but to have involved a number of pulses that were exceptionally hot, i.e. that the temperature of the plume fluctuates over time intervals of a few million years (White and Lovell 1997). The size and duration of the shelf uplifts were used to constrain the magnitude and velocity of these pulses (Shaw Champion et al. 2008; Hartley et al. 2011). Thus, the stratigraphy of sedimentary rocks on the ocean retains a record of the mantle pulsing (White and Lovell 1997; Hartley et al. 2011).

Where uplift raises continental margins above sea‐level, their consequent sub‐aerial erosion causes relatively coarse‐grained sediments to be deposited on adjacent sub‐marine shelves. These pulse‐drive uplifts can have significant commercial consequences: for example, the Forties oil‐field is dependent on sandy reservoir rocks that resulted from continental lithosphere uplift at ~55 Ma, marking the arrival of a major thermal input (Lovell 2010). Furthermore, the changes in the elevation of the Greenland–Faeroes–Iceland and Scotland ridge over millions of years have controlled the deep‐water overflow of the Denmark Straits (Wright and Miller 1996; Nisbet et al. 2009; Poore et al. 2009, 2011).