Reading On the mid-ocean ridge, which, like the seam of a baseball in the oceans, runs around the globe, new ocean crust is created by rising lava. A puzzle has so far been how to make the lava in water at temperatures near freezing to flow for several miles. Based on electron microscopic investigations of lava rock, a British-American research team now concludes that hot steam plays a major role in this process. Ian Ridley of the United States Geological Survey and his colleagues present their findings in the journal Nature (Vol. 426, p. 62). Until now, it has been assumed that a pressure at the seafloor of more than one hundred times the atmospheric pressure can not cause so much water vapor that a significant interaction between water vapor and lava occurs. In addition, on the outside of the lava would quickly form a thick glassy protective layer, which prevents any further contact between water and lava.

But Ridley and his colleagues have found structures in lava rock from the seabed that they believe have been formed by the contact of very hot water vapor with lava. The rock is traversed by the remnants of small cavities that were probably created by water vapor bubbles, but later collapsed because of the high pressure. This thesis is supported by a salt deposit on the walls of the cavity remains.

The researchers believe that water vapor can penetrate from below into the lava as it flows over the young, rugged ocean floor. The water trapped in small ruts and holes is evaporated and rises into the lava. Ridley and colleagues estimate that a 0.5 centimeter thick layer of water, despite the high pressure that raises the boiling point of the water to a few hundred degrees Celsius, is transformed within five minutes into a ten centimeter thick layer of water vapor. The water vapor bubbles rising into the lava then reduce the friction of the lava with its already solidified outer skin and thus allow the lava to flow for several kilometers, even in terrain without a great incline.

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Axel Tilleman

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