Alive under the ash rain | Environment| All topics from climate change to conservation | DW | 19.05.2015
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Alive under the ash rain

Thirty-five years after the eruption of Mount St. Helens, experts explain how volcanoes affect biodiversity - both positively and negatively. With several active volcanos around the world, implications are broad.

On May 18, 1980, Mount St. Helens unexpectedly erupted, spewing lava and smoke and triggering a massive avalanche. The raw power of nature unleashed killed 57 people and destroyed hundreds of homes, along with infrastructure including bridges, railways and highways. As the deadliest and most economically destructive volcanic event in the history of the United States, it also destroyed the ecology of the area, creating a wasteland that wiped out the plants and animals of the region.

In Nicaragua, Telica is the most active volcano. Again and again, it spews debris skyward and dusts nearby villages in fine ash. Over the past month, there have been up to 30 eruptions a week, some throwing hot rocks, gas and ash up to 400 meters, according to the Nicaraguan Geological Institute.

And Telica isn't the only volcano making itself known at the moment. Turrialba in Costa Rica has been keeping geologists on alert recently. Volcanic activity isn't unusual and while reports of huge cloud-like plumes of smoke and ash pushing into the sky or slow flowing lava make an impression, the only outbreaks to attract publicattention are those that pose a threat to human and environmental health. They occur maybe once or twice a year.

The #link: Catalog of Active Volcanoes,# which lists which fire-spitting mountains have erupted within the last 10,000 years, says an average of 70 are active each year.

Hawaii is high on that list. The archipelago has the most active volcano on earth: Kilauea on Big Island. Its lava has been flowing uninterrupted since 1983. Kilauea is part of a chain of volcanoes, spread over a hot area - or hotspot - below the earth's crust, says #link: Fraser, #a volcanologist at the Australian National University.

"In general, we see a lot of volcanoes around the edges of the continental plates," she said. "These plates are cold hard rock that sits on top of the more liquid hot layer underneath, and where two plates meet, one slips under the other and starts to melt. As it does, some of the molten rock can break back up to surface as volcanoes."

Significant impact on nature

This molten matter has the first and most violent effect on the ecosystem in the immediate vicinity. #link: volcanologist Olafur Arnalds# says the effects can range from temporary disturbance to total destruction of the existing surface.

The ecosystem needs up to 150 years to compensate a relatively small sedimentary deposit resulting from an eruption of about 10 to 20 centimeters. If deposits grow up to more than 70 centimeters, the existing soil is covered and it takes several hundred years for new soil to form. Recovery depends heavily on surviving plants, the availability of new seeds and their undisturbed development.

But flowing lava and liquefied sediment have been part of "some of the most detrimental volcanic disasters in history," Arnalds added. The eruption of Mount Pinatubo in the Philippines, is a case in point.

Mount Pinatubo seen from above

It might look serene, but Mount Pinatubo in the Philippines can blow its top

On 15 June, 1991 a cloud of ash shot 34 kilometers into the sky, and molten rock flowed down the mountain, travelling as far as 16 kilometers from the crater. The eruption left the adjoining Marelle Valley covered in up to 200 meters of sediment, and the ash cloud darkened the region's skies for days.

The subsequent ash rain, supported by a simultaneous typhoon, fell on almost every Philippine island and spread as far as the South China Sea, Vietnam, Cambodia and Malaysia. At least 875 people were killed.

Changing landscapes

According to Olafur Arnalds, deposited sediment, ash or rocks can change the soil structure of a certain region permanently and impact crop yield or livestock, which die as a result of inhaling volcanic ash. The eruption of Mount St. Helens in 1980 caused a seven percent fall in income among farmers close to the volcano.

Eruptions can also contaminate rivers, making it hard for fish to survive, blocking entrances to rodent's burrows and coating birds' nesting sites in ash. As Arnalds explained, the effects can be long lasting.

Mount St. Helens

Mount St. Helens erupted 35 years ago

"Small mammals returned to Mount St. Helena's severely impacted zones within years," he said, adding that they relied on ecosystem remnants and elements of the recovering system.

The eternal mass extinction myth

The effects of volcanic eruptions are even said to have played a role in a mass extinction event 252 million years ago. According to the scientific journal Science, a string of blasts known as the Great Dying, wiped out numerous species between the Permian and Triassic periods. Over the next 10,000 years the resulting levels of carbon dioxide caused dramatic ocean acidification that wiped out 96 percent of all marine species.

But the influence of volcanic eruptions on the environment is not always devastating. If the amount and type of ejected and deposited material is right, they can even have a positive effect on nutrients in the soil, and can be advantageous for vegetation and people.

Ceridwen Fraser offers Hawaii as an example. "Each island is a volcano of a different age, and the oldest ones tend to have the greatest diversity of life," she said. "Without those volcanoes, the islands would not exist and the complex and diverse ecosystems they house would also not exist."

Hawaii lava stream from Kilauea

Slow flowing lava is not an uncommon sight on Hawaii's big island

In colder regions, she adds, the heat and steam of volcanoes can also prove positive by melting snow and ice cover to provide a place for certain species to live.

"In Antarctica, the species that will have benefited from volcanoes in the long term are mainly plants and invertebrates. The relatively warm spots in otherwise cold lands would have been a bit like Noah's Ark, housing survivors that would later go out and repopulate other areas as they gradually became free of ice as well."

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