Volcanoes and atmospheric carbon dioxide

Are volcanoes a source of atmospheric carbon dioxide? This question is a point of
controversy concerning the greenhouse effect and its potential impact on global
warming. In this activity you will learn how volcanic eruptions contribute to atmospheric
carbon dioxide, the greenhouse effect, as well as global temperatures. Initially, when a
volcano erupts, it ejects many different types of material into the air including a variety
of gasses and ash (small particles of dust). Among these gasses ejected into the
atmosphere are gasses such as water vapor and carbon dioxide. Both of these gasses
are greenhouse gasses and can contribute to the greenhouse effect. Carbon dioxide
levels in the atmosphere have been increasing—now scientists are studying whether
volcanoes are playing a significant role in the greenhouse effect.

  1. Which contributes more carbon dioxide per year to the atmosphere: volcanic
    eruptions or human activity?
  2. Does a volcanic eruption cause a warming or cooling effect?
    Large volcanic eruptions deposit water vapor (H2O), carbon dioxide
    (CO2), sulfur dioxide (SO2), and other gasses into the environment.
    Volcanoes can also put great amounts of ash (small particles of dust)
    into the air. As you have learned, carbon dioxide and water vapor are
    greenhouse gasses and can contribute to global warming. Water can
    combine with other volcanic gasses such as hydrochloric acid (HCl)
    and hydrofluoric acid (HF) to fall as acid rain. Volcanoes also emit
    sulfur dioxide (SO2) which converts to a fine mist of particulates that
    migrate high into the atmosphere. These sulfur dioxide particulates are called sulfate
    aerosols, and they reflect sunlight back into space. Sulfate aerosols encourage the
    formation of high clouds which also reflects sunlight back into space. Therefore
    Explore and Explain
    Engage Your Thinking
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    aerosols and clouds reduce the amount of warming and cause the atmosphere to cool.
    Sulfate aerosols tend to stay in the upper atmosphere for long periods of time (months
    or even years) until they finally are brought to earth in the form of sulfuric acid. The
    volcanic ash in the atmosphere also blocks sunlight from reaching the surface of the
    earth causing the air to cool. (The ash eventually falls to the ground.)
  3. What greenhouse gasses are added to the atmosphere during a volcanic
    eruption?
  4. Explain how a volcanic eruption cools the atmosphere.
    Other factors need to be considered in the study of volcanic eruptions and their impact
    on the atmosphere. All volcanoes are not the same. The type of eruption is dependent
    on the circumstances that cause the volcanic activity. Volcanoes created by hotspots in
    the ocean are rarely explosive and do not eject much ash. Eruptions taking place at
    geographic plate boundaries, however, can be very explosive with much ash. Also, the
    types and amounts of gasses ejected by each type of volcano differ. Table 1 shows
    gasses ejected by three different volcanoes situated at three different geographic
    locations. Make a bar graph that shows the amount of H2O, CO2, and SO2 emitted by
    the three different volcanoes.
    Table 1. Examples of Volcanic Gas Compositions. Source: USGS
    Volcano
    Tectonic Style
    Temperature
    Kilauea Summit
    Hot Spot
    1170°C
    Erta` Ale
    Divergent Plate
    1130°C
    Momotombo
    Convergent Plate
    820°C
    H20 37.1 % 77.2 % 97.1 %
    C02 48.9 % 11.3% 1.44%
    S02 11.8% 8.34% 0.50%
  5. In general, volcanoes eject which gas the most?
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  6. Which volcano ejected the greatest percentage of carbon dioxide?
    Many people argue that volcanic eruptions are a major cause of carbon dioxide levels in
    our atmosphere. In reality, volcanic eruptions contribute very little to the atmosphere’s
    carbon dioxide levels. Below are the USGS carbon dioxide emission estimates for
    volcanic and human activity (Table 2).
    Table 2. Yearly Average Carbon Dioxide Emissions
    From Volcanoes: 145 – 225 million tons of CO2
    From human activity: 30 billion tons of CO2
    Let’s express the volcano amount as about 200,000,000 or 2.0 X 108
    tons
    The human activity amount is 30,000,000,000 or 3.0 X 1010 tons
    Imagine that you will make a bar graph to compare the carbon dioxide contribution of
    volcanoes and human activities. (You will not actually make the graph.)
    Using a scale with one centimeter representing 1.0 X 108
    tons, your bar graph will
    represent the carbon dioxide contributed by volcanoes with a bar 2 cm. high.
    Volcanoes emit 2.0 X 108
    tons of CO2 per year which gives you a bar that is 2 cm. high.
  7. Calculate the height of the bar representing carbon dioxide from human activity.
  8. How important are volcanoes in adding carbon dioxide to the atmosphere?
    Mount Pinatubo is a volcano that lies near a divergent plate boundary in the Philippines.
    In June of 1991, Mount Pinatubo violently erupted, and this eruption is now on record as
    the second largest volcanic eruption of the twentieth century. The eruption had ten
    times the explosive power of the 1980 eruption of Mt. St. Helens in the state of
    Washington. Within two hours of the major Pinatubo eruption, gasses and ash reached
    high into the atmosphere. During the following two weeks, the sulfate aerosols created
    by the blast circled the globe and at the end of a year, the entire atmosphere of the
    earth was filled with a layer of sulfate aerosols ejected from the eruption.
    Extend Your Thinking
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    The sulfur aerosols created by the Pinatubo blast reflecting solar energy (heat and light)
    back into space and decreased temperatures around the world in 1992 and 1993. In
    spite of rising amounts of greenhouse gasses and the presence of an El Nino event
    (factors that should warm the atmosphere), the sulfate aerosols reduced global
    temperatures in 1992 and 1993 by about 0.4 to 0.5ºC—a global cooling effect. The
    United States experienced its third-coldest summer in seventy-seven years.
    The 1815 eruption of theTambora Volcano in Indonesia created an even larger global
    cooling effect. Global temperatures were lowered by as much as 3ºC. The year 1816
    was known as the year without summer in many parts of Europe and North America.
    Many Midwest states experienced snowfall in June and frost in July.
  9. What effect do the sulfate aerosols formed by volcanoes have on global
    temperatures?
    Draw an erupting volcano. In your drawing, draw and label the materials that are ejected by the volcano. Under your drawing, explain what effect each material might
    have on the temperature of the atmosphere.
    Apply What You Have Learned
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    10.Which contributes more carbon dioxide per year to the atmosphere: volcanic eruptions or human activity?
    11.Does a volcanic eruption cause a warming or cooling effect?
    12.What is the major cause of cooling after a volcanic eruption?
    13.Please explain how your ideas and thinking about greenhouse gases has
    changed.

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