volcanic

Mount Unzen has been spewing out volcanic ash, gas, and rock today.

St Vincent is a lush, volcanic island.

And it mentions something about volcanic eruptions too.

Molten rock or lava, flowing up through the earth's crust, which means, of course, that volcanic activity there can't be explained simply by plate tectonics.

So, how do we explain these volcanic anomalies, these exceptions to the general rule?

Well, back in 1963, a geophysicist by the name of Wilson came up with a hot-spot theory to explain how this particular type of volcanic activity can occur.

You're getting a chain of volcanic islands where the hot plume melts through the crust under the Pacific Ocean at one point after another with active volcanoes on the younger islands that are now just above the plume.

Incidentally, volcanic islands may seem small, but the island known as the Big Island Hawaii is one of the tallest topographic features on the planet.

Now, the Plume Hypothesis provides a pretty elegant explanation for a volcanic anomaly, like the Hawaiian Islands.

Even the model supporters are uncomfortable claiming that it explains every volcanic anomaly.

The plants were preserved under a thick ash fall from a volcanic eruption.

The younger terrain is the result of tectonic and volcanic forces.

How can volcanic activity occur so far from a plate boundary?

Canadian geophysicist Tuzo Wilson realized that this age progression could result if the islands were formed on a surface plate moving over a fixed volcanic source in the interior.

Wilson suggested that the long chain of volcanoes stretching northwest from Hawaii is simply the surface expression of a long-lived volcanic source located beneath the tectonic plate in the mantle.

They as the plate moved slowly northwest, new volcanic islands would have forms as the plate moved over the volcanic source.

The most recent island, Hawaii, would be at the end of the chain and is now over the volcanic source.

The oceanic volcanic islands and their hot-spot trails are thus especially useful for geologist because they record the past locations of the plate over a fixed source.

Age estimates ranging from four billion years for Mars’s southern highlands to a few hundred million years in the youngest volcanic areas were obtained in this way.

It's quite possible that this is due to volcanic eruptions, because volcanic eruptions often emit gases.

So this too suggests ongoing volcanic activity.

Iceland sits on a volcanic structure known as the Mid-Atlantic Ridge.

Reykjavik, the capital of Iceland, is entirely heated by geothermal energy derived from volcanic heat.

They occur primarily in regions of recent volcanic activity as hot, dry rock; natural hot water; or natural steam.

Their settlements contain exotic objects such as seashells, stone bowls, and artifacts made of obsidian (volcanic glass), all traded from afar.

On occasion, animals and plants have been preserved after becoming immersed in tar or quicksand, trapped in ice or lava flows, or engulfed by rapid falls of volcanic ash.

In the early twentieth century, the American ecologist Frederic Clements pointed out that a succession of plant communities would develop after a disturbance such as a volcanic eruption, heavy flood, or forest fire.

Ancient demands for obsidian (a black volcanic rock useful for making mirrors and tools) led to trade with Armenia to the north, while jade for cutting tools was brought from Turkistan, and the precious stone lapis lazuli was imported from Afghanistan.

Also included will be any variations that have arisen from volcanic activity, solar activity, and, possibly, human activities.

The exact role of other factors is much more difficult to pinpoint―for instance, Teotihuacán’s religious significance as a shrine, the historical situation in and around the Valley of Mexico toward the end of the first millennium B.C., the ingenuity and foresightedness of Teotihuacán’s elite, and, finally, the impact of natural disasters, such as the volcanic eruptions of the late first millennium B.C.

Around this time, the largest of these centers, Cuicuilco, was seriously affected by a volcanic eruption, with much of its agricultural land covered by lava.

The hard volcanic stone was a resource that had been in great demand for many years, at least since the rise of the Olmecs (a people who flourished between 1200 and 400 B.C.), and it apparently had a secure market.