Wednesday, 1 June 2016

Nature's Amazing Spectacle: Island Formation by an Underwater Volcano

Blog Contents; Who am I?
Wonderful and amazing things happen in nature all the time - auroras (dancing northern lights) are probably the most spectacular of them all.  Earthquakes, volcanoes, tsunamis, hurricanes, lightning are some of the manifestations of nature's gigantic energy.  Luckily, we now understand the reasons behind such amazing spectacles but they happen often enough to lose their wow factor.  
A rare event, even though well-understood, still has the power to excite.  Remember the first picture of the blue earth taken by astronauts from space and the excitement that it had caused.

Live observation of new land being formed in the South Pacific Ocean by the eruption of an underwater volcano (a seamount) was accidentally made in 2006.  We all know that there are underwater volcanoes and they are as active as the run-of-the-mill volcanoes we see on land.  These extinct volcanoes, seamounts and guyots, are part of the structure of the oceanic crust.  In fact, the highest mountain in the world is a seamount - Hawaii's Mauna Kea, a dormant volcano that is more than 30,000 feet tall measured from its base - that is taller than Mount Everest!



As two continental plates move apart from each other (generally about 2 cm per year amounting to 2000 km in 100 million years), it opens up a crack in the earth's crust. Molten magma extrudes out from the crack, cools to form ocean ridge on either side of the crack (rift valley).  Lot of the loosely deposited ridge is weathered by ocean currents and in time, the continental plates move further apart and also the ridge loses its height.  
Seamount and guyots which are raised oceanic crust due to extinct volcanoes move with the plates.  If originally the top of the seamount had risen above ocean water level then the wave action would have eroded the top and the flat top seamount becomes a guyot.  As they move away from the plates, their distance below the ocean water level increases - they sink.

If the volcanic eruption deposits enough magma, the lava (solidified magma) can stick out of the ocean surface and forms a temporary island.  Such islands do not always last for ever and most disappear after a period of days to moths or a few years.

How an island is formed is depicted by the following figure
Surtseyan Eruption-numbers.svg

1: Water vapour cloud     2: Cupressoid ash
3: Crater        4: Water       5: Layers of lava and ash
6: Stratum     7: Magma conduit    
8: Magma chamber      9: Dike

Regular volcanic activity can create permanent islands - Hawaiian islands are the best example of a series of islands created by underwater volcanic eruption. 

The wow factor comes from the uniqueness of an observation when such an island is being formed in real time.  
This is exactly what had happened in 2006 in the South Pacific near the Vava'u Islands in Tonga.  I describe the amazing experience of the crew of the yacht Maiken in their own words:


The crew of the Yacht Maiken were sailing through the South Pacific near the Vava'u Islands in Tonga when they noticed that the water in the distance has gone a strange colour.  
The crew documented the phenomenon in a series of remarkable pictures as they sailed into the formation to investigate, not realizing that a volcano was erupting just a few miles away
As the crew approached, the sea mysteriously turned to stone as the volcano pushed up new land



A beach in the middle of the sea: Before long, the land mass had bubbled up out of the ocean.  One of the crew, Fredrik Fransson told Discover magazine'We looked out and, in front of us, it was as if there was no more sea. It was 'like the Sahara with rolling hills of sand as far as the eye could see'.
They hadn't run ashore, but had instead found themselves surrounded by a huge raft of floating pumice stone



'Then we saw a black pillar (of smoke) shooting up into the air, and we understood that it had to be a volcano,' said Mr Fransson, adding that they navigated cautiously towards the plume.

'It was kind of a smouldering, smokey stuff. It looked like coal, and when there was an eruption, we could see the new material piling up on it.'
They then watched as an island grew before their eyes with each explosion in an area where there should be an underwater seamount called Home Reef.



Underwater eruptions are thought to occur dozens of times a year, but normally in remote areas or at depths inaccessible to humans. 
Eight months after the island's birth, some of it had washed up in Queensland, Australia, some 2,000 miles away.

A more recent island formation happened in December 2014.

In late December, an undersea volcano in the Polynesian island kingdom of Tonga began erupting. About 60 kilometers (40 miles) north of Tongatapu, the two small islands of Hunga Tonga and Hunga Ha'apai sit atop a large seamount. These volcanic islands stand just 128 and 149 meters (420 and 490 feet) above sea level. The new eruption occurred just offshore of Hunga Ha'apai. 
According to news reports, fishermen spotted signs of an eruption on December 19, and a photographer on the island of Tongatapu observed steam plumes on the horizon on December 24. Dense cloud cover prevented other remote observations for several days.
The following natural-color images from December 29 and 31, 2014, show the waters around Tonga, Hunga Tonga, and Hunga Ha'apai, as observed on by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite. A white plume rises into the sky on both days.  The plume extended 3 kilometers (2 miles) into the sky. The discolored water nearby suggested an underwater release of gases and rock or the disturbance of sediment by the eruption.
Hunga Ha'apai is part of the Tonga-Kermadec volcanic arc and is part of the very active Pacific Ring of Fire. The last reported eruption occurred in 2009.

island1.jpg

December 29, 2014 Photograph of the two Islands


island2-rex.jpg
December 31, 2014 Photograph of the two Islands with a new island formation

I hope this blog has provided a glimpse of an exciting natural phenomenon. 
I am grateful to Dr Prabhakara Bhatt for bringing this matter to my attention.
Post-script:  As one would expect, formation of an island by underwater volcanic eruption is not a unique event and has been happening throughout Earth's history.  It is the observation of such an event in detail that I felt was worth writing about.  Professor Gerry Peterson (of UMASS) has pointed out to me that the island of Surtsey off the southwest coast of Iceland formed in a series of more or less continuous underwater volcanic eruptions during 1963 to 1967.  Surtsy (meaning Surtur's Island  - Surtr being a fire giant of Norse mythology), at the end of 1967 was 174 metres tall and 2.8 square kilometers in area. Here is a picture of Surtsey as it looks now. 
Modern Surtsey

The island has a protective cover of solidified magma and is expected to survive for a few centuries.  Its current area is 1.4 km^2 and has a height of 155m.












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