Environmental factors controlling the palagonitization of the Surtsey tephra, Iceland

The Surtsey tephra was formed between Nov. 14, 1963 and April 4, 1964 in the phreatic phase of the Surtsey eruption. Since then, the tephra has been inspected annually to follow the expected process of consolidation and palagonitization. In 1969 the first signs of palagonitization of the basaltic glass were observed. The process was clearly connected to the formation of a hydrothermal anomaly established within the tephra pile in 1968. Heat transfer probably occurred by convection of vapourized sea and meteoric water, the heat source being feeder dykes and shallow intrusions. The palagonitization of the Surtsey tephra during 1969-1976 is inferred to have proceeded at l00°C and 1 atm. except in the uppermost 0.5-2 m where the process has operated down to at least 40° C. The rate of palagonitization-consolidation is evaluated as a function of temperature and time. Probably most of the tephra pile within the hydro­thermal anomaly was palagonitized in less than 1-1 ½ years; in 1976 possibly some 64% of the total tephra pile had become palagonitized. The conditions for the process of palagonitization in general are briefly discussed.