The Formation of Palagonite Tuffs
basalt glass of the Surtsey tephra is easily altered, and the rock formed
is called palagonite tuff (móberg). The conversion causes the
tephra particles to stick together. This alteration process is called
The first sign of palagonite tuff on the
surface was in November 1969. It had formed inside the hydrothermal
area at a temperature of 60-70°C over a period of approximately
2.5 years. Since then the formation of palagonite tuff on the surface
has been closely observed, and research has also been done on the drilling
core from 1979.
The palagonitization is primarily dependent
on the temperature of the water in the rock. At a temperature of 100°C
and above, the Surtsey tephra has consolidated into palagonite tuff
in approximately one year or even only a few months. This is a much
more rapid palagonization than was expected. At lower temperatures,
the rate of conversion is slower. At 40-50°C, for example, it has
taken 4-8 years. At present, most of the tephra above sea level has
consolidated into hard palagonite tuff. It is also believed that submarine
palagonization has been considerable.
chemical reactions take place when basalt glass transforms into palagonite.
Cations are released from the glass and in their place the glass binds
to water causing the iron to oxidize. The cations, particularly Si,
Al, Ca, Na and Mg, can then form cavity fillings in the rock. A total
of ten new kinds of newly formed minerals have been discovered in the
palagonite tuffs in Surtsey. The most common are analsime, phillipsite,
tobermotite, smektite and anhydrite.
The Surtsey eruption has led to a better
understanding of how the palagonite tuff mountains were formed in the
Ice Age. Research on the alteration of tephra has yielded important
information on palagonization. In this regard, Surtsey can be compared
to a gigantic laboratory. The latest discovery in these research projects
is from a study of microorganisms in the rock. Results show that certain
bacteria species dissolve the basalt glass in the tephra, thereby increasing
the rate of palagonite formation.
a slideshow on palagonite formation in Surtsey
P. Jakobsson – email@example.com)