Let's think big. Really big. Imagine a flood of lava oozing out of an enormous fissure in the crust. Then imagine that it keeps leaking sporadically for a million years. You've just conjured up the basic basaltic blueprint for the 200,000 square-kilometer Columbia River plateau, a vast expanse of basalt (defined) in Oregon and Washington. Click here for beautiful 3D image of this area.

The same thing happened to form the Deccan 'traps', a field of basalt in western India that reaches a thickness of 3.5 kilometers in some places.

If you gun the magma-maker to the max, perhaps you can imagine the incomprehensibly huge Siberian traps, a 1.5 million-cubic-kilometer lava leak that sprung out of the earth over roughly a 10-million-year period. (In comparison, Mt. St. Helens blasted out a measly one cubic kilometer in 1980.)

The so-called 'flood basalts' arose when basaltic lava oozed through a fissure in the earth and flooded across the landscape. Basalt makes a high-temperature lava with a low silica content that flows fast and far -- up to 100 kilometers per hour. It is this lack of viscosity (defined) that enables basaltic lava to form the massive "flood basalt provinces" we're discussing. Lava that's more gluey would make steeper piles. Those make volcanic mountains like the Andes in South America.

The only flood basalt in recorded history spilled 12 cubic kilometers of lava across Iceland in 1783, releasing enough gas to cause Benjamin Franklin to write about a wierd, dense "dry fog" in Europe that contained no water. The gases, containing fluoride from the eruption, settled on the pastures in Iceland, poisoning the critical sheep herds and causing starvation that killed 20 percent of the population. And remember, that was peanuts in terms of flood basalts.

A climate for extinction
Flood basalts have sparked interest because some seem to coincide with the periodic extinctions in the fossil record. It's easy to speculate that such a flow of hot rock could produce enough heat, gas and dust and general commotion to affect the atmosphere and alter the climate. Recall that Mt. Pinatubo, (a water pistol when compared to the fire hose that is a flood basalt) but still the largest eruption of the 20th century, caused a 0.5 degree (Celsius) global cooling when its ash reflected sunlight back to space. In contrast to that cooling, these incomprehensibly larger lava flows could release greenhouse gases that trapped heat and raised planetary temperatures. Either phenomenon, if large enough, could alter the climate enough to extinguish species. The Why Files covered climate investigations here.

Did they or didn't they?
But just because these gargantuan eruptions could affect climate does not mean they did. The jury is still out, the evidence is mixed, and the cliches are coming hot and heavy. For example, the Deccan traps occurred at exactly the same time as the Cretaceous-Tertiary extinction that wiped out relatives of Tyrannosaurus rex. However, there's also good evidence that the extinction was caused by a comet or meteorite that kicked up dust, causing a global winter. (We will come back to this later in the course.) Either phenomenon -- or a combination -- could have demoralized the dinosaurs

Oceanic crust is slowly "recycled," being formed at the mid-ocean ridges, transported in conveyor-belt fashion across the ocean floor, and finally destroyed along "subduction zones," where slabs of oceanic crust re-enter the earth's mantle and are consumed.

Courtesy of NGDC (National Geophysical Data Center) and NOAA (National Oceanic and Atmospheric Association).

(see "Sudden Death by Lava" in the bibliography).

Oddly, recent research indicates that the even-larger Siberian traps, which occurred between 238 and 230 million years ago, coincide quite well with the Permian/Triassic extinction (defined).

Down at the Mid-Atlantic Ridge
While we're talking about large fissures in the Earth, let's remember that this process is going on right now at roughly 40,000 kilometers of underwater junctions between tectonic plates. At the Mid-Atlantic Ridge, for example (the junction that runs through Iceland and accounts for its volcanism), magma wells up and spreads out in both directions, forming new ocean floor that moves east and west across the ocean, conveyor-belt fashion. (Here is another pretty picture.) In addition, the number of volcanoes hidden beneath the ocean surface could be far greater than are found on land.

In the grand scheme of things, in fact, volcanism is the rule rather than the exception. All told, about 80 percent of Earth's surface -- seafloor and land -- originated as a flow of molten rock from deep inside earth.

Carjackings? Wildfires? Earthquakes? Think California has enough problems without having to worry about a cataclysmic eruption? Think again...