Wednesday, June 28, 2017

Pumice and Pumice Rafts

Pumice collected from beach on Norfolk Island (May 2017)

Having recently visited Norfolk Island (located in the S. Pacific midway between Australia and New Zealand) I was struck by the amount of pumice on the beaches and was told it came from an underwater volcano off New Zealand.
It probably relates to a major undersea volcano, the previously little-known Havre Seamount in the Kermadec Islands of New Zealand, which erupted in 2012.
A raft of pumice floating on the sea 
The huge volume of molten rock, produced by the eruption, resulted in a large area of floating pumice known as a PUMICE RAFT. This originally covered a surface of 400 square kilometres (150 square miles). 
The raft divided by a boat sailing through 
The thickness of the raft may have been as great as 3.5mt (11ft) but reduced to around 0.5mt (1ft 8in) within a month. It soon spread to a continuous float of between 7,500 and 10,000 sq. miles (19,000 and 26,000km2) and within three month dispersed to an area of more than twice the size of New Zealand. 
Beach at Norfolk Island dotted with pumice
Reports followed of pumice being found of the beaches of Tasmania and eastern Australia.
Dr Carey University of Tasmania) said pumice rafts were believed to have been a primary means for the transport of sedentary marine species between continents in prehistoric times.
Huge raft see from space
Photos of the PUMICE RAFT taken after a volcanic eruption in the South Pacific give an indication of its immense size both from water level and from space.
(Courtesy of the USGS and Smithsonian Institute).

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