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Geosciences Column: From the desolate to the diverse, a story of volcanic succession

18 Jul

When a volcano erupts and spews lava onto the surrounding terrain, it is merciless in its destruction. All that is green on the land is engulfed in flame, or buried by an insurmountable mass of molten rock. Whatever charred remains of what lies beneath it will not see the light of day once the lava cools, turning the landscape into a barren black mass of solid basalt.

But volcanoes around the world are not barren basaltic masses. On the contrary, many volcanic slopes are teeming with life. Much of the Hawaiian archipelago is a tropical paradise, its older lava fields thick with forest and foliage. Likewise, Iceland’s flotilla of fiery peaks hasn’t rendered the land completely barren. So how does life return to the scene after an eruption?

Hardy grass on Surtsey’s black sands. (Credit: Ragnar Sigurdsson (arctic-images.com via imaggeo.egu.eu)

Hardy grass on Surtsey’s black sands. (Credit: Ragnar Sigurdsson (arctic-images.com via imaggeo.egu.eu)

The answer lies in a process known as succession. One by one, starting with the hardiest life forms, the lava is recolonised by wind-blown spores and seeds that have managed to make it from areas unharmed by the latest eruption. Over time, the growing community of plants attracts animals that bring further seeds to the site, either clinging desperately to their fur, or deployed stealthily in their droppings.

A long-term investigation of two very different volcanoes has revealed what allows the earliest arrivals to take hold: Surtsey, an isolated volcanic island in the North Atlantic, and Mount St. Helens, a once towering and peak in Washington State. The findings are published in Biogeosciences, an open access journal of the European Geosciences Union.

Surtsey’s arrival in 1963 (left, credit: NOAA) and Mount St Helens during the 1980 eruption (right, credit: Austin Post/USGS)

Surtsey’s arrival in 1963 (left, credit: NOAA) and Mount St Helens during the 1980 eruption (right, credit: Austin Post/USGS)

Surtsey emerged off the Icelandic coast in 1963 amid billowing plumes of ash and steam. Erupting from underwater, Surtsey created its own island – a fresh field of lava that has been consistently monitored since 1990. Mount St Helens erupted violently in 1980, after a catastrophic landslide triggered a volcanic blast so large that the volcano’s entire north flank, together with 370 square kilometres of forest, were obliterated. The resulting fields of pumice, tephra and lava provided a blank canvas for life to start afresh in the area.

Surtsey and Mout St Helens differ in terms of their age, the way they’re isolated, their climate and their size. But, despite these differences, scientists Roger del Moral and Borgþór Magnússon found the way vegetation first established itself followed the same fundamental principles, regardless of where it set up camp.

It’s all down to two different filters: isolation and stress. Isolation creates the biggest filter; meaning only the most well-travelled species can take hold. Then stress further sorts the species that can survive – well-travelled weaklings wouldn’t stand a chance in a place with incredibly poor fertility.

Birds make life a little easier for all involved, particularly in coastal areas, where an entire colony of birds can become established. These birds import nutrients from the surrounding sea by consuming fish from and depositing their waste on land. On Surtsey, these nutrient imports have meant the richest plant life has developed where the bird colonies are.

On Mount St Helens, winds carrying nutrient-laden dust created the first fertile material. This let a group of flowering plants known as lupines take hold and, after several cycles of lupine blooms, the ground became much more fertile. The areas where lupines bloom are now the most species rich.

Vegetation on Surtsey (top, credit: Borgþór Magnússon) and Mount St Helens (bottom, credit: Roger del Moral). Images on the left are areas where the rate of succession is slow, those on the right detail areas with a faster succession rate.

Vegetation on Surtsey (top, credit: Borgþór Magnússon) and Mount St Helens (bottom, credit: Roger del Moral). Images on the left are areas where the rate of succession is slow, those on the right detail areas with a faster succession rate.

In a world where environments are rapidly changing and species are having to move into new territories to adapt, these findings can help shed light on how plants could keep pace with the change as they shift from one site to the next.

By Sara Mynott, EGU Communications Officer

Reference:

del Moral, R. and Magnússon, B.: Surtsey and Mount St. Helens: a comparison of early succession rates, Biogeosciences, 11, 2099-2111, doi:10.5194/bg-11-2099-2014, 2014.

 

Imaggeo on Mondays: Turkey’s cotton castle

7 Jul

This week, Imaggeo on Mondays is brought to you by Josep Ubalde, who transports us to a wonderful site in western Turkey: a city of hot springs and ancient ruins dubbed cotton castle, after the voluminous white rocks that spread from the spring’s centre…

Pamukkale is lies in Turkey’s inner Aegean region, within an active fault that favours the formation of hot springs. The spring’s hot waters were once used by the ancient Greco-Roman city of Hierapolis, the remains of which sit atop Pamukkale. The entire area – city, springs and all – was declared a World Heritage site in 1988.

Travertine terraces in Pamukkale, Turkey (Credit: Josep M. Ubalde via imaggeo.egu.eu)

Travertine terraces in Pamukkale, Turkey (Credit: Josep M. Ubalde via imaggeo.egu.eu)

The materials that make up Pamukkale are travertines, sedimentary rocks deposited by water from a hot spring. Here, the spring water follows a 320-metre-long channel to the head of the travertine ridge before falling onto large terraces, each of which are about 60-70 metres long.

The travertines are formed in cascading pools that step down in a series of natural white balconies. These travertines are 300 metres high and their shape and colour lend them the name Pamukkale, meaning “cotton castle”.

At its source, the water temperature ranges between 35 and 60 degrees Celsius, and it contains a high concentration of calcium carbonate (over 80 ppm). When this carbonate-rich water comes into contact with the air, it evaporates and leaves deposits of calcium carbonate behind. Initially, the deposits are like a soft jelly, but over the time they harden to form the solid terraces you see here.

Putting Pamukkale into perspective (Credit: Josep M. Ubalde)

Putting Pamukkale into perspective (Credit: Josep M. Ubalde)

These travertines have been forming for the last 400,000 years. The rate they form is affected by weather conditions, ambient temperature, and the duration of water flow from the spring. It is estimated that 500 milligrams of calcium carbonate is deposited on the travertine for every litre of water. Today, thermal water is released over the terraces in a controlled programme to help preserve this natural wonder. You can no longer walk on them, but they are beautiful to behold.

By Josep M. Ubalde, Soil Scientist, Miguel Torres Winery

Imaggeo is the EGU’s open access geosciences image repository. Photos uploaded to Imaggeo can be used by scientists, the press and the public provided the original author is credited. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. You can submit your photos here.

Imaggeo on Mondays: Quartz lawns and crystal flowers

26 May

Petrologists spend a large part of their time peering down microscopes at wafer thin slices of rock to work out what they’re made of and how they were formed. What lies on the other side of the lens can be an incredibly beautiful pattern, a kaleidoscope of colour, or stark bands of black and white, all of which provide clues to the rock’s history, and the history of the landscape it came from. Bernardo Cesare, enthusiastic photographer and professor of petrology at the University of Padova, Italy, has captured some fantastic images of these slender rock sections, including the incredible image of ocean jasper, below.

Ocean jasper under the microscope – 30 micrometres thin and almost entirely quartz. (Credit: Bernardo Cesare via imaggeo.egu.eu)

Ocean jasper under the microscope – 30 micrometres thin and almost entirely quartz. (Credit: Bernardo Cesare via imaggeo.egu.eu)

Ocean jasper is a variety of jasper found only in Madagascar and is increasingly sought after as a precious stone, and with that, decent rock samples are hard to come by. “I have long been searching for affordable samples of ocean jasper, until I saw a necklace in a market stall. I cut all the beads, prepared thin sections from them, and put them under the microscope,” says Cesare.  “They turned out to contain a microscopic garden of quartz flowers in a fine-grained silica matrix. In places some coarser crystals form ‘rosettes’ in a lawn of fibrous quartz too.”

Jasper jewelery – it looks even more lovely under the microscope, don’t you think? (Credit: Tess Norberg/Nova Design)

Jasper jewellery – it looks even more lovely under the microscope, don’t you think? (Credit: Tess Norberg/Nova Design)

Ocean jasper is made up of many minute orbs, just a few millimetres in diameter, known as spherulites. They form when silica-rich volcanic rocks change from being glassy to crystalline, and are saturated with silica in the process. This crystallisation occurs in arrays of thousands of fibrous, needle-like crystals. “They can grow as perfect spheres, but where they’re too close to one another the growing spherulites impinge on each other,” Cesare explains. This close clustering causes the spherulites to have sharp boundaries where they meet, something clearly seen in Cesare’s snap of the crystal structure.

Even though almost everything in the image (the exception being the small black dots, which are opaque minerals) is made of quartz, a rainbow of colours can be seen. These rainbows are known as interference colours, and they appear when polarized light passes through a crystal. So what creates this rainbow?

When white light, first polarized by a filter, passes through the crystals of a rock, it is split in two components that travel at different speeds. These components interfere with the crystal structure in different ways depending on their wavelength and the crystal’s orientation. When light emerges from the crystal and is filtered for the second time, some wavelengths are suppressed, so the colour of the light is no longer white. Cesare explains why: “the interference colour depends on the type of mineral (more precisely on its birefringence), on its thickness, and on its orientation. This is why crystals of the same mineral (quartz) may display different colours in my image: because they have different optical orientations!”

There are even ways to test out this tool at home: “even without a slice of rock, readers can test how interference colours emerge using two “crossed” polarizing filters (for example two orthogonal lenses of some sunglasses) and placing a stretched piece of plastic bag between them,” says Cesare.

A shiny sample of ocean jasper (Credit: Druzy Macro)

A shiny sample of ocean jasper (Credit: Druzy Macro)

“Polarized light is one of the fundamental tools of a geologist: with a polarizing microscope and a thin section we can recognize different minerals without the aid of more sophisticated and expensive analyses. Looking at colours and at their changes, at the shapes and contours of mineral grains, at their sizes and mutual relationships, not only can we understand which minerals a rock contains, but also in which sequence they formed, if some deformation occurred during or after their crystallisation, if they were transformed into other minerals and, qualitatively, at which pressure and temperature conditions the rock originated or evolved.” All these observations form the basis for more detailed research, such as, working out how many millions (or billions) of years ago the rock formed.

You can find out more about ocean jasper and Cesare’s photographic style over at National Geographic and on Geology In Art. You can also find more of his photography over at www.microckscopica.org.

By Sara Mynott, EGU Communications Officer

Imaggeo is the EGU’s open access geosciences image repository. Photos uploaded to Imaggeo can be used by scientists, the press and the public provided the original author is credited. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. You can submit your photos here.

Imaggeo on Mondays: Villarrica Volcano

14 Apr

This week’s Imaggeo on Mondays highlights the vulnerability of Villarrica’s slopes and zooms in on the volcano’s spectacular crater…

Villarrica, one of the largest stratovolcanoes in Chile, is also one of the country’s most active. The volcano is iced by glaciers that make the mountain a stunning scene, but also a dangerous one. The glaciers cover some 30 square-kilometres of the volcano and, during an eruption, the snow and ice melts to form lahars (rapid mud flows that move at 30-40 kilometres per hour). These flows present a formidable hazard to the towns that flank the volcano.

Villarrica from above – if you look closely, you can see the traces of lahars on the volcano’s northwest flanks. (Credit: NASA Earth Observatory/Jesse Allen/Robert Simmon)

Villarrica from above – if you look closely, you can see the traces of lahars on the volcano’s northwest flanks. (Credit: NASA Earth Observatory/Jesse Allen/Robert Simmon)

Villarica’s crater spans some 250 metres and takes the form of steeply sloping basalt. The cherry on the volcanic cake (and just out of shot here) is the lava lake at its summit. Villarrica is constantly degassing through this lava lake – a process that releases pressure below the surface. Without it, eruptions would be much more violent.

Peering into the crater of Villarrica Volcano, Chile. (Credit: Dávid Karátson via imaggeo.egu.eu)

Peering into the crater of Villarrica Volcano, Chile. (Credit: Dávid Karátson via imaggeo.egu.eu)

Imaggeo is the EGU’s open access geosciences image repository. Photos uploaded to Imaggeo can be used by scientists, the press and the public provided the original author is credited. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. You can submit your photos here.

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