Volcanoes: Creators and destroyers of life

The world's largest active volcano, Mauna Loa, began erupting on the island of Hawaii on Sunday. Fissures sent lava flows slowly rolling down the 4,169 meter-high (13,677 feet-high) mountain, but so far no one is in danger.

The eruption at Mauna Loa joins neighboring volcano Kilauea, which has been erupting for more than year.

Mauna Loa last erupted in 1984. "We were waiting for this eruption for many years. Until the 1950s, it was the most active volcano on Earth. But since then, something has changed in its interior," Thomas Walter, a geophysicist at the German Research Centre for Geosciences, told DW.

Volcanic eruptions form fertile landmasses like Hawaii

Despite their destructive power, volcanoes can also be a force of life.

The Hawaiian Islands, 137 in total, were all formed by volcanic activity some 40 to 70 million years ago. The landmasses were created from multiple volcanic eruptions underneath the seafloor. Magma burst out of the Earth's mantle or lower crust before eventually reaching the ocean's surface.

Once the magma reaches the Earth’s surface, it becomes known as lava. In the case of the Hawaiian Islands and other volcanic islands, such as Iceland and Santorini, lava has cooled and assembled over time to create land.

"All Pacific islands have volcanic foundations, having begun life as ocean-floor volcanoes similar to those sputtering into life along the deep-ocean ridges and in places  — often called hotspots  — in the middle of giant crustal plates," Patrick Nunn, a geography professor at the University of the Sunshine Coast, Australia, told media outlets after the Mauna Loa eruption.

What's more, the rich vegetation and fertile lands of Hawaii owe much to volcanic eruptions. Volcanic ash is rich with elements like magnesium and potassium that act as natural fertilizers.  

Volcanoes helped create life on Earth…

According to Petr Broz, a planetary scientist at the Czech Academy of Sciences, the gases emitted from volcanoes have arguably shaped planets more than the landmasses they have created.

Volcanoes release huge amounts of water vapor and carbon dioxide into the atmosphere when they erupt. In the long term, these greenhouse gases are incredibly effective at heating up the atmosphere, contributing to global warming.

"Without volcanoes, you have no strong source [that emits] greenhouse gases into the atmosphere, at least on planets that have no man-made emissions," Broz told DW.

"The emission of greenhouse gases from volcanoes was very important for life on Earth. Without volcanoes, we would have a weaker greenhouse effect, making the planet much colder," he added.

In fact, Broz explained, the level of volcanic activity on different planets correlates with the planetary temperatures and their ability to host life.

"Mars has no active volcanoes and barely any atmosphere, making it extremely cold. Venus is incredibly hot because of greenhouse gases released into the atmosphere. But Earth is just right [for life]," he said.

…but also destroy life

The destructive reputation of volcanoes is rooted in reality. Eruptions around the globe have done untold damage on local ecosystems.

Sometimes eruptions are so severe they can even affect the entire planet's climate. An eruption at Mount Tambora in Indonesia in 1815 killed up to 84,000 people, but also caused the 1816 "year without a summer" in the northern hemisphere.  

But this pales in comparison to so-called supervolcano eruptions earlier in history. About 74,000 years ago, a huge eruption at present-day Lake Toba in Sumatra, Indonesia, caused a winter that lasted six to 10 years around the globe. The volcanic winter resulted in a reduction in the average temperature of the Earth’s surface by 3–5 °C (5.4–9.0 °F).

The reason? Huge amounts of volcanic gases and ash clogged the atmosphere, dimming sunlight. The effects of the Toba eruption on global climate were so severe experts believe there was a significant reduction in the total human population in the aftermath.

Humanity emits 60 times more carbon dioxide than volcanoes

Closer to home, scientists hope to understand the future of the Earth's climate by measuring gases released from volcanic eruptions into the atmosphere.

"For a long time, we wanted to know whether volcanoes or humans are larger producers of greenhouse gases. Now it's obvious that humans produce more greenhouse gases than volcanoes," said Broz.

Broz refers to data from the Carbon Dioxide Information Analysis Center (CDIAC) showing that human activity emits 60 times more carbon dioxide than volcanoes each year. Each volcanic eruption emits huge amounts of greenhouse gases, but they are too infrequent to rival the emissions caused by human activity.

"We have 1,500 active volcanoes on Earth, plus around 40,000 to 50,000 inactive volcanoes that emit gases. But they produce tiny amounts of greenhouse gases compared to what humans produce," said Walter.

Edited by: Carla Bleiker