The Earth seems to have been smoking a lot recently. Volcanoes are erupting in Iceland, Hawaii, Indonesia, Ecuador and Mexico right now. Others, in the Philippines and Papua New Guinea, erupted recently but seem to have calmed down. Many of these have threatened homes and forced evacuations. But among their spectators, these eruptions raise this question: Is there such a thing as a season for volcanic eruptions?

While volcanoes may not have "seasons" as we know them, scientists have started to discern intriguing patterns in their activity.

Eruptions caused by a shortened day

The four seasons are caused by the Earth's axis of rotation tilting toward and away from the sun. But our planet undergoes another, less well-known change, which affects it in a more subtle way, perhaps even volcanically.

Due to factors like the gravitational pull of the sun and moon, the speed at which the Earth rotates constantly changes. Accordingly the length of a day actually varies from year to year. The difference is only in the order of milliseconds. But new research suggests that this seemingly small perturbation could bring about significant changes on our planet - or more accurately, within it.

A study published in the journal Terra Nova in February showed that, since the early 19th century, changes in the Earth's rotation rate tended to be followed by increases in global volcanic activity. It found that, between 1830 and 2013, the longest period for which a reliable record was available, relatively large changes in rotation rate were immediately followed by an increase in the number of large volcanic eruptions. And, more than merely being correlated, the authors believe that the rotation changes might actually have triggered these large eruptions.

Altering the spin of a planet, even by a small amount, requires a huge amount of energy. It has been estimated that changes in the Earth's rotation rate dissipate around 120,000 petajoules of energy each year - enough to power the United States for the same length of time. This energy is transferred into the Earth's atmosphere and subsurface. And it is this second consequence that the Terra Nova authors believe could affect volcanoes.

The vast quantities of energy delivered to the subsurface by rotation changes are likely to perturb its stress field. And, since the magma that feeds volcanic eruptions resides in the Earth's crust, stress variations there may make it easier for the liquid rock to rise to the surface, and thereby increase the rate of volcanic eruptions.

The Terra Nova study is far from conclusive. Nevertheless, the idea that minute changes to the Earth's spin could affect volcanic motions deep within the planet is an intriguing one.

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