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A Closer Look

Volcanoes Change the World
volcanic eruption changes the local What were the effects of volcanic haze global temperatures by a few tenths of a
A landscape, that much is obvious. What from Tambora around the entire world? degree for two or three years. The cooling
is not so obvious are the worldwide changes There were fantastic, brightly colored sunsets did take place, but the actual El Chichon
that can happen just because of the eruption from the added haze in the stratosphere. On contribution to the cooling is not clear
of a single volcano. Perhaps the most dis- the other hand, it was also cooler than usual, because of other interactions. Earth may
cussed change brought about by a volcano presumably because of the reflected sunlight have been undergoing global warming from
occurred back in 1815–1816 after the erup- that did not reach Earth’s surface. It snowed the greenhouse effect, for example, so the El
tion of Tambora in Indonesia. The Tam- in New England in June 1816, and the cold Chichon cooling effect could have actually
bora eruption was massive, blasting huge continued into July. Crops failed, and 1816 been much greater. Other complicating
amounts of volcanic dust, ash, and gas high became known as the “year without summer.” factors such as the effects of El Niño or
into the atmosphere. Most of the ash and More information is available about La Niña (see chapter 23) make changes
dust fell back to Earth around the volcano, the worldwide effects of present-day volcanic difficult to predict.
but some dust particles and sulfur dioxide eruptions because there are now instruments In June 1991, the Philippine volcano
gas were pushed high into the stratosphere. to make more observations in more places. Mount Pinatubo erupted, blasting twice as
It is known today that the sulfur dioxide However, it is still necessary to do a great much gas and dust into the stratosphere as
from explosive volcanic eruptions reacts with deal of estimating because of the relative El Chichon had about a decade earlier. Dust
water vapor in the stratosphere, forming tiny inaccessibility of the worldwide strato- from Mount Pinatubo remained in Earth’s
droplets of diluted sulfuric acid. In the sphere. It was estimated, for example, that atmosphere for the next 10 years. The haze
stratosphere, there is no convection, so the the 1982 eruption of El Chichon in Mexico from such eruptions has the potential to cool
droplets of acid and dust from the volcano created enough haze in the stratosphere to the climate about 0.5°C (1°F). The overall
eventually form a layer around the entire reflect 5 percent of the solar radiation away result, however, will always depend on a pos-
globe. This haze remains in the stratosphere from Earth. Researchers also estimated sible greenhouse effect, a possible El Niño or
for years, reflecting and scattering sunlight. that the El Chichon eruption cooled the La Niña effect, and other complications.

Mt. Garibaldi
CANADA
Vancouver
U.S.A.
Mt. Baker
Vancouver Island
Glacier Peak MONTANA
Seattle
WASHINGTON
Mt. Rainier
Columbia
Mt. Adams
Juan de Fuca Portland Plateau Basalts
Plate Mt. St. Helens
Mt. Hood
OREGON
Mt. Jefferson
IDAHO
Three Sisters
North American Plate
Pacific Plate Crater Lake
Mt. Shasta
Lassen
Peak
NEVADA UTAH

CALIFORNIA
San Francisco
Mono Craters
0 200
Kilometers

FIGURE 19.25 The Juan de Fuca Plate, the Cascade volcanoes, and the Columbia Plateau Basalts.

19-17 CHAPTER 19 Building Earth’s Surface 493