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February 26, 2004

A weekly feature provided by scientists at the Hawaiian Volcano Observatory.

Eruptions help cool interior of Earth ? but there?s a long way to go

People frequently ask, ?What?s with all these eruptions I hear about? Is volcanic activity increasing?? Indeed, a plot of reported eruptions over the last 200 years shows ever-increasing numbers, but it is very likely that this is due to increased interest and ease of worldwide communication rather than increased volcanic activity.

For example, the major decreases in the numbers of reported eruptions over the last 200 years occurred during the two world wars, when everyone had far more pressing matters to report. There were even news blackouts imposed on reporting the occurrence of eruptions during wartime. Here in Hawai`i, the press was prohibited from reporting Mauna Loa?s 1942 eruption, purportedly to keep the eruption from acting as a homing beacon for the enemy.

A more unbiased way to examine eruption frequency is to consider only reports of large, explosive eruptions over the last 200 years. The effects of such eruptions are more widespread; thus they were more likely to be reported even when they occurred in remote areas. The frequency of these large eruptions has been remarkably constant.

Since the start of comprehensive reporting of volcanic activity, the number of volcanoes actively erupting has remained quite steady at 50 to 70 per year. There are usually about 20 volcanoes erupting at any given time on Earth. Some of those currently active are Colima in Mexico, Erebus in Antarctica, Stromboli in Italy, Dukono in Indonesia, Fuego and Santa Maria in Guatemala, Karymsky and Shiveluch in Russia, Sakura-jima in Japan, Soufriere Hills at Montserrat in the Caribbean, Nyiragongo in central Africa, Tungurahua in Ecuador and, of course, our own Kilauea. More information on these volcanoes and current activity can be found at the Smithsonian Institution?s Global Volcanism website:

Many more volcanoes are currently exhibiting signs of unrest, which can include increased levels of seismicity, deformation of the ground surface, and volcanic gas emissions. About 1500 volcanoes have erupted in the last 10,000 years, and that?s just counting the ones on land. If we include young seafloor volcanoes, the estimate could go up by a factor of at least 100!

The huge number of undersea volcanoes is at least partly due to the large amount of heat available at mid-ocean spreading centers, where the thin oceanic crust is torn apart as tectonic plates move away from each other.

There are mainly two internal heat sources that drive plate tectonics and volcanic eruptions: heat left over from the formation of the earth, and decay of radioactive elements within the earth. Volcanic eruptions account for a large proportion of the internal heat that is dissipated from the interior of the earth.

Are volcanoes helping to heat up the surface of the Earth? Not really. The internal heat released by volcanoes is negligible compared to solar radiation. As a matter of fact, large, explosive eruptions can actually lower, rather than raise, surface temperatures for several years. These eruptions blast huge clouds of ash and gas into the atmosphere, which can reflect solar radiation away from Earth. However, there has been speculation recently about undersea eruptions providing enough heat to influence ocean-warming cycles.

Are all these volcanoes releasing enough heat to speed our beautiful planet toward its eventual fate -- a world without volcanoes or plate tectonics, like present-day Mercury or Mars? Volcanism played a major role in the early history of these planets, but their small size relative to Earth resulted in the loss of internal heat at a much faster rate than Earth.

It is harder than you might think to figure out at what rate the Earth is cooling. We can measure the amount of heat being emitted at and near the surface at many places and come up with an estimate of the global heat flow, but figuring out how much is stored and generated in the interior is truly a head-scratcher. Suffice it to say that we will have the awesome force of volcanic activity on our planet for countless future generations.

Activity update

Eruptive activity at the Pu`u `O`o vent of Kilauea Volcano continued unabated during the past week. Most lava flows have been at the lower end of the rootless shield complex along the Mother?s Day lava tube, at the 2200-2300-foot elevation south of Pu`u `O`o. Some lava has reached the surface along the upper part of the Mother?s Day tube and from the south base of Pu`u `O`o. Vents within the crater of Pu`u `O`o remain incandescent. No active flows are on Pulama pali or the coastal flat below Paliuli. No lava is entering the ocean.

Two small earthquakes were felt on the island during the week ending early February 26. Both occurred on February 22. The first was located 6 km (4 miles) south-southwest of Pu`u `O`o at a depth of 10 km (6 miles). The magnitude 3.2 shake was felt at Hale Pohaku and Hilo. About 7 hours later, a magnitude 3.5 earthquake shook the west side of the island and was felt from Honaunau to Kalaoa and also on the Hamakua Coast at Papa`aloa. This off-island earthquake was located 45 km (28 miles) west of Ho`okena at a depth of 42 km (26 miles).

Mauna Loa is not erupting. The summit region continues to inflate slowly. Seismic activity remains very low, with no earthquakes located in the summit area since early February 19. P<> Visit our website ( for daily volcano updates and nearly real-time earthquake information. skip past bottom navigational bar

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Updated: March 9, 2004 (pnf)