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Why Kilauea is not a killer volcano

Hawaiian volcanoes are slow and steady eruptions that have been bubbling away for tens of thousands of years and will continue to do so in the future.
Lava from a fissure slowly advances to the northeast on Hookapu Street after the eruption of Hawaii's Kilauea volcano on May 5, 2018 near Pahoa, Hawaii. (Getty Images)

Spectacular images of molten lava devouring homes and cars, while red hot fountains of fire spew boulders and deadly gasses into the sky on Hawaii's Big Island make the volcanic activity look deadly. But compared to other types of volcanoes around the world, Hawaii is pretty benign.

Disastrous eruptions in history

History has recorded incredible eruptions such as Mount Vesuvius in 79 AD ,which destroyed the towns of Pompeii, the 1883 eruption of the Krakatau in Indonesia which was heard thousands of kilometres away and the violent outburst of Mt. St. Helen's in 1980.

Those were instantaneous explosions that blew entire mountaintops into the air and devastated the landscape for hundreds of square kilometres. Forests were laid flat, and in some cases, thousands of people were killed literally where they stood.   

In 1883, Krakatau, a volcano in Indonesia, erupted and destroyed much of itself. It left behind Rakata Island (at the back), a truncated rim of the original volcano. Anak Krakatau, or "Child of Krakatau” (in the front) is a post-caldera cone that formed in 1928 and has been active since. (Volcanological Survey of Indonesia, 1979)

In contrast, Hawaiian volcanoes are slow and steady eruptions that have been bubbling away for tens of thousands of years and will continue to do so in the future. And while the destruction to the local buildings and roads is serious, no one is caught by surprise because the lava moves so slowly, you can literally step aside and let it flow by.

In fact, the very images we are getting from Hawaii are from people standing not far away. Local tour companies even offer helicopter flights over the lava flows. So the best way to deal with a Hawaiian eruption is to simply evacuate the local area.

How volcanoes are formed

Most volcanoes around the world happen along the boundaries between the huge plates that make up the crust of the Earth. There are about a dozen of these continent-sized pieces that are constantly jostling for position like pieces of ice on a lake during spring breakup. And like the ice, the plates of the Earth are floating on hot molten liquid layers of the Earth's interior.

Plume rises from the Halemaumau crater, illuminated by glow from the crater's lava lake, within the Kilauea volcano summit at the Hawaii Volcanoes National Park on May 9, 2018. (Getty Images)

When plates pull apart, as they are doing down the middle of the Atlantic Ocean, new material oozes up from below. Iceland is a result of this spreading activity which is why the island is always volcanically active. Icelandic volcanoes can spew a lot of ash in the air as we saw recently when airlines had to re-route their planes, but they are not explosive.

Colliding plates, or subduction zones, such as along the west coast of North America, the Mediterranean, or Indonesia, is where one plate rides over top of the other. The plate that gets pushed down into the interior of the Earth is melted by the heat, then it pops back up, poking a hole in the crust above, so you end up with volcanoes such as Mt. St. Helens and Vesuvius.

In this case, the crust that was pushed down carries water with it, which is turned to steam, creating tremendous pressure below ground. When the pressure is released during an eruption, the volcano becomes a champagne bottle, literally blowing its top into the sky. These so-called Vesuvian eruptions are the most violent ever recorded and they happen in a matter of minutes.

Hawaiian volcanoes

Hawaiian volcanoes on the other hand are different because they are happening in the middle of a plate, a hot spot under the Pacific Ocean that is believed to be the top of a gigantic plume that reaches deep into the mantle of the Earth. This theory was pioneered by Canadian Geologist J. Tuzo Wilson, who suggested that the hot magma has literally burned a hole through the crust and is oozing out onto the surface. There is very little water in this magma, so it doesn't have the explosive force of a Vesuvian eruption.

Resident Stacy Welch inspects lava next to a destroyed home located 250-feet from her home, which remains standing in the aftermath of eruptions from the Kilauea volcano on Hawaii's Big Island on May 7, 2018 (Getty Images)

At the same time, the Pacific plate has been moving over the hot spot in a northerly direction, so more than one hole has been punched through the crust. The other islands in the Hawaiian chain, Oahu, Maui, Kauai and so on to the north, have moved away from the hot spot and are now dormant. That is also why the new activity on the big island is towards the southeast.The plate is still slowly moving north.

Eventually, Kilauea will go quiet and a new island will appear to the south. Already, a volcanic seamount is erupting underwater called Loihi, which may become that new island.

Living with natural disasters is a way of life in many parts of the world. People live in hurricane zones, within reach of forest fires, or on fault lines where earthquakes are frequent. For the people of Hawaii, they have to accept the fact that they live on an active volcano that is not going to stop erupting anytime soon.

The best way to deal with it is evacuate the area, but they don't have to evacuate the entire island. Every now and then someone will have to shout, "Walk for your lives! The lava is coming!"

About the Author

Bob McDonald

Bob McDonald is the host of CBC Radio's award-winning weekly science program, Quirks & Quarks. He is also a science commentator for CBC News Network and CBC TV's The National. He has received 12 honorary degrees and is an Officer of the Order of Canada.

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