Before and After: How do Streams and Rivers Behave Before and After a Volcanic Explosion?

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Author: Janice VanCleave


How do streams and rivers behave before and after a volcanic explosion?


  • Scissors
  • Ruler
  • Heavyweight aluminum foil
  • Cookie sheet
  • Pencil
  • 3-ounce (90-ml) paper cup
  • Marble
  • Tap water
  • Book


Before and After

  1. Cut a 10-inch × 10-inch (25-cm × 25-cm) piece of aluminum foil.
  2. Fold the piece in half, lengthwise, twice, forming a strip 10 inches × 2.5 inches (25 cm × 6.25 cm).
  3. Six inches (15 cm) from one end of the strip, cut 3/4-inch (l.9-cm) slits on both edges.
  4. Bend the sides of the 6-inch (15-cm) section upward.
  5. Raise the 4inch (10-cm) end of the foil and bend it down over the edge of the cookie sheet to create a ramp.
  6. Position a marble at the end of the channel formed by the aluminum foil.
  7. Use the point of the pencil to punch a small hole in the side of the paper cup just above its bottom edge.
  8. Place your finger over the hole in the cup, and fill the cup with tap water.
  9. Use the book to support the cup on the top edge of the cookie sheet, with the hole in the cup pointing toward the channel.
  10. Remove your finger and allow the water to flow out of the hole in the cup.
  11. Observe any movement of the marble as the water flows down and out of the channel.


The water pouring out the small hole slowly moves down the channel, around the marble, and out into the cookie sheet. The marble is affected only slightly, or not at all, by the small stream of flowing water.

Before and After


The small amount of water flowing down the paper channel does not have enough force to push the marble out of its way. The water hits the marble and is redirected around its sides. The small amount of water simulates the gentle flow of clear water from rainfall and slow-melting snow down the slope of an inactive volcano.


What would happen if a larger amount of water was released from the cup? Repeat the original experiment, replacing the cup with a cup that has a hole slightly larger than the diameter of the pencil. The water released from this cup represents the massive water flow produced by the quick melting of snow and ice by heat from a volcanic explosion.


Some volcanoes, such as Mount St. Helens and Krakatoa, erupt so violently that the earth shakes, causing landslides. Dark clouds of hot ash, rock, and dirt can be blasted upward from the vent for many miles. Mudflows can form by the mixing of fast-melting snow and ice with the ash, rock, and dirt that rain down onto the slopes. Demonstrate the formation of mudflows by performing the following outdoor activity:

  • Lay a cookie sheet on the ground and raise one end about 2 inches (5 cm) by putting soil under the edge of the sheet.
  • Cover the sheet with a layer of soil.
  • Fill a 1-gallon (4-liter) jug with tap water.
  • Tilt the water jug so that its mouth is about 6 inches (15 cm) from the raised end of the cookie sheet Photographs taken before and after the water is poured onto the soil can be used as project displays.


Before and After

  1. The appearance of Mount St. Helens was strikingly different before and after it exploded, blowing about one cubic mile of its northern slope into the air. Find out more about the geological changes in the rivers and streams caused by Mount St. Helens' eruption on May 18, 1980. How long did the mudflows and flood waters last? Were all the changes in the streams and rivers permanent?
  2. Many volcanoes erupt each year on earth. Mudflows are one kind of hazard that threaten the lives of the millions of people that live near volcanoes. Find out more about the hazards created by volcanic eruptions, such as lateral blasts that can overwhelm people before they can flee, violent undersea eruptions that cause sea waves, poisonous gases that can suffocate, and hot ash that can bury people.
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