The Vellir thermal field in the Reykholtsdalur valley belongs to the Reykholt thermal system.The hot springs are distributed along two lines.The main thermal activity follows the 1.5 km long Vellir line, which has a general trend near N15°E.The other line is divided into two short northwesterly trending segments on each side of the valley, the Sturlu-Reykir and Hagahús lines.The Vellir geyser is the largest hot spring.All significant hot springs are close to boiling and the accumulated discharge is 33l/s.The base temperature of the field is about 130°C.Geological and geophysical evidence suggests that the regional flow towards the field is controlled by at least two northeasterly trending faults.They are intersected by open northerly trending fractures.The major hot springs are located at or close to the intersections.
Summary Sea-water from Deception Island was found to contain 0·55–1·48 mg Mn 1 −1 and 10·2-64·3 mg Si 1 −1 . Reaction of Deception Island basalt and sea-water at 190 °C and 500 bars simulated the measured water composition but leaching experiments suggest that much of the Mn etc. may derive from local volcanic ash. Mn and Mg in thermal waters at Reykjanes have concentrations compatible with equilibrium with components of montmorillonite present as an alteration mineral of average composition . However, Fe is controlled by equilibrium with sulphides. Flux calculations based on these and other data place upper limits on hydrothermal Mn input to the oceans of 5–36×10 11 g yr −1 and Mn accumulation in metalliferous sediments of 2–9×10 11 g yr −1 .
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