Movement may be only two to six inches per year.When plates move in relation to each other, Earthquakes and Volcanoes are produced.Because plates move, albeit very slowly over time, the positions of continents change over time. Plate Tectonics essentially refers to the rearranging of Earth’s continents, moving them closer to or farther away from the Equator or the Poles. Ice ages have occurred only when Earth’s shifting crustal plates carried the continents from tropical latitudes to more poleward positions.
Plate TectonicsGlacial evidence in present day warm areas of Africa, Australia, South America, and India indicate that these regions experienced an ice age about 250 million years ago.Areas containing these ancient glacial features were joined as a single “supercontinent” located toward the South Pole.The plates eventually spread apart, some landing in tropical and subtropical locations.Shifts in plates also affected oceanic circulation, altering the transport of heat and moisture and hence the climate.Climate changes brought about by plate movements are extremely gradual and happen on a scale of millions of years.
Volcanic Activity and Climate ChangeVolcanic activity is a plausible explanation for some aspects of climate variability.Big volcanic eruptions emit huge quantities of gases and fine-grained debris into the atmosphere.Greatest eruptions inject material high into the stratosphere.This material spreads around the Globe and remains for many months or even years.Suspended volcanic material does filter outa portion of the incoming solar radiation.This, in turn, lowers temperatures in the troposphere and stratosphere. (Ben Franklin used this idea when explaining the unusually cold winter of 1783-1784, relating it to the eruption of a large Icelandic volcano.)The impact on climate of a single volcanic eruption, no matter how great, is relatively small and short lived.Many great eruptions would have to occur, closely spaced in time, for volcanism to have a pronounced effect on climate.
“Year Without a Summer”The Northeastern USA and Canada and Western Europe experienced unprecedented cold spells from May – September 1816.heavy snow in Junefrost in July and AugustThis year without a summer followed the 1815 eruption of Mount Tambora in Indonesia. (Similar, although less dramatic effects, have been associated with other great explosive volcanoes, including Indonesia’s Krakatoa in 1883.)Mount Tambora, a 13,000 foot tall volcano, erupted from April 7 – 12, 1815. It violently expelled more than 24 cubic miles of volcanic debris. Over the course of the next year, this debris was carried around the Earth’s atmosphere by global winds. Eventually some of the material reached the atmosphere over New England where is blocked out some the Sun’s rays during the summer of 1816.
Other Recent Volcanic EruptionsMount St. Helens (1980), Washington State, USALarge volume of volcanic ash had significant local and regional effects for a short time. This fine ash settled out in a relatively short time.
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