Surtsey erupted from November of 1963 to June of 1967. At the end of the eruption the new island was about 2,500 feet (800 m) in diameter. The island has not grown since the last eruption. The volcano is made of lava flows and tephra on a submarine (under water) base of pillow lava. The subaerial (under air) lava flows serve as a protective cap on part of the island. The part of the island that is made of only tephra is prone to wave erosion. As tephra is removed by waves the island will shrink in size.
Source of Information:
Decker, R., and Decker, B., 1989, Volcanoes: W.H. Freemnan, New York, 285 p.
Steve Mattox
Surtsey is featured in a number of volcano books because it popped to the surface of the Atlantic Ocean and was able to be studied pretty closely almost from the first moments.
Prior to the eruption that location was known to be shallow so it wasn't a huge surprise; the shallow water was actually the summit of an undersea volcano that wasn't quite at the surface yet. The first eruptions were very explosive because of the mixture of hot lava and ocean water, and even after the island built above sea level, water was still able to seep through the ash to make more explosions. Eventually, however, the vent got sealed off from the ocean and the eruptions became non-explosive Hawaiian-style lava fountains instead of steam explosions. In fact, explosive water-lava eruptions are now called "Surtseyan" after Surtsey. A number of times water would suddenly gain access to the vent and instantly the activity would go from quiet Hawaiian-style fountaining to explosive Surtseyan explosions. This created quite a hazard to those studying the volcano.
There is a book called:
Surtsey, The New Island in the North Atlantic, by S. Thorarinsson, published by Viking Press of New York.
Additionally, there is a section on Surtsey in Volcanoes of the Earth by Fred Bullard (1976).
Surtsey is still around. Volcanoes of the World (by Tom Simkin and Lee Seibert) lists its last activity as 1967. It is now being attacked by waves, and if it does not erupt again it may eventually disappear. Many times during the early days of its eruption it was nearly washed away by the waves. That is because it was originally mostly ash (formed by the explosive interaction of erupting lava and ocean water). As soon as the cone had built to the point that water could no longer gain access to the vent, the eruption style changed to more Hawaiian style, with lava fountains producing lava flows. These hardened flows are much more resistant than the earlier-produced ash, and they guarantee that the island won't be washed away very quickly.
Scott Rowland
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