Science Lesson: Volcanoes
You’ve probably heard in the news about volcanic eruptions, or you might remember when Mount St. Helens erupted. Perhaps you’ve even seen an active volcano. Although they are often a destructive force, volcanoes are an amazing facet of creation. They come in a variety of shapes, sizes, and eruption types.
Volcanoes erupt when magma, red-hot liquid rock, seeps up through a vent in the earth. More violent eruptions occur when pyroclastic material (a mixture of magma, rocks, ash, and hot gases) is exploded upward by pressure caused by underground gases and magma.
When magma flows above the surface of the earth, it is called lava. Usually lava changes from bright red to duller red, gray, or black as air causes it to cool and solidify.
Volcanic eruptions vary in size and display. There are six common types of eruptions, with differing features. Plinian eruptions usually have thick lava and high gas content. They can shoot pyroclastic material high into the air, moving at hundreds of feet per second. These eruptions can last for hours or even days. Hawaiian eruptions are not usually very explosive; instead, they produce streams of slow-moving lava. An interesting feature of Hawaiian eruptions are “fire fountains”, huge fountains of magma being spewed into the air. These fountains last anywhere from a few minutes to a few hours. Strombolian eruptions put on an impressive display but are not usually very dangerous. During these eruptions, lava is shot fifty to a few hundred feet into the air and is accompanied by booming noises. These eruptions do not produce much lava flow. Vulcanian eruptions do not have much lava flow either, but they tend to be larger than Strombolian ones. They produce a lot of ash and spit out “bombs” of hard pyroclastic material. Hydrovolcanic eruptions occur when water vapor hits hot magma and gases, and forms huge steam clouds that rise from the volcano. Fissure eruptions occur when magma leaks up through a long crack in the ground. They are associated with “curtains of fire” magma being spewed up to a small height all along a fissure.
There are also different shapes and sizes of volcanoes. Stratovolcanos are usually very high, with pointy tops. They are formed by repeated explosions, usually Plinian, and by slow-moving lava. Eruptions from these volcanoes are usually very large but occur infrequently. Mount Vesuvius, which buried the Roman city of Pompeii in 79 AD, is a stratovolcano. Shield-type volcanoes are usually spread out over a large area and have gently sloping sides. They are caused by minor explosions (usually Hawaiian) and erupt more frequently than stratovolcanoes. Most of the major volcanoes in Hawaii are shield volcanoes. Scoria Cones are the most common volcano type, usually caused by Strombolian eruptions. They are shaped like upside-down cones, with slightly squished tops. Scoria cones usually erupt only once.
For more information about volcanoes and other geological structures, consider The Geology Book, by Dr. John Morris.
Science Lesson: Volcanic Eruption Experiment
You can demonstrate a volcanic eruption using some simple household items. Kids usually have a great time doing this experiment, and may want to repeat it several times!
To make a big eruption, use a small plastic bottle (the size 20-oz soft drinks come in works well). Fill the bottle halfway (1 to 1.5 cups) of vinegar. To start the eruption, drop a baking soda “bomb” into the bottle—wrap one tablespoon of baking soda into a small piece of tissue paper, tying the ends with string.
You should see an instant eruption—”lava” will spurt out of the mouth of the bottle. The baking soda, a base, neutralizes the acid in vinegar. This releases carbon dioxide gas, which causes the fizzing action in your volcano.
For a more exciting eruption, try sticking a cork loosely in the mouth of the bottle. The force inside the bottle should cause this “pyroclastic material” to shoot up into the air!
If you want your volcano to look more realistic, use clay or playdough to make a “mountain” around the bottle. Or, if you’re working outside, you might want to use dirt and pebbles. You can also add red food coloring to the vinegar solution to make it look more like lava.
Use our Amazing Volcanoes kit for a variety of other fun and informative experiments.
Science Lesson: Erosion
Have you ever seen a canyon and wondered how it was formed? Canyons, as well as many other geological formations, are the product of erosion. Erosion is the process by which material is worn away from the earth’s surface, and can be caused by many different factors, such as wind, animals, and even plants. One of the main causes of erosion, however, is water. Rain and rivers can wear down the land over a long period of time, by washing away the soil and rock little by little. Often water seeps into cracks in the rock and then freezes and thaws. This expanding and contracting of the water can break the rock.
Water rushing at great speeds can cause significant erosion in a small amount of time. While workers were draining water from Lake Powell in Arizona, the force of the water ripped apart the concrete in the drain tunnel and in one minute created a hole in the surrounding rock 32 feet deep, 150 feet long and 40 feet wide. There are three main processes that cause rapid erosion of this kind:
Cavitation: This occurs when tiny vacuum bubbles in rapidly moving water explode inwardly, pounding the rock with great force.
Plucking: Sometimes rushing water can “pluck” loose blocks from the bedrock and carry them away.
Kolking: Underwater tornadoes, called “kolks”, act just like a tornado in the air. They can lift and carry away large chunks of rock.
Often erosion will result in strange shapes, like the arches that can be seen in Arches National Park in Utah. These unique structures are formed when water dissolves one kind of rock but does not affect the surrounding rocks.
To learn more fascinating information about erosion, read The Geology Book by Dr. John Morris.
Science Lesson: Flood Demonstration
Water is one of the most forceful factors in erosion. What would happen to the landscape if it were all drowned in rushing waters? You can demonstrate the catastrophic effect of a global flood using a large dishpan and a few other items. Read Genesis 6-8 to your children and discuss the magnitude of the Flood in Gen. 7:1-24. Explain how prior to the Flood there was a great water layer in the atmosphere and another great water layer under the crust of the earth. During the Flood both of these were opened up to cover the entire earth with water. The amount of water needed to cover a 5,000-foot tall mountain in 40 days would be the equivalent of raining 1 inch per minute.
Prepare the “earth” model by placing 3-4 water balloons in the bottom of the dishpan to represent the water layer under the surface. Then build a landmass over the balloons by covering them with gravel, sand, and soil in successive layers. Form the landmass to make hills over the balloons. Finally place a few plastic animals or seashells at various places on the land. Now you are ready to flood the earth. Puncture one of the balloons with a long pointed object and observe the effect on the landmass. Then get a large bucket or hose and pour water on the land at the rate of 1-2 inches per minute. Again observe what happens to the land surface. Continue to break the balloons and pour water on the land until it is fully under water.
You may have to let your flooded “earth” sit in the sun for several days before the floodwaters recede. (The wait won’t be as long if your pan had some small holes for drainage.) Record your observations. How did the land change? What happened to the animals? Did you get some “fossils”?
Science in the News: Mount St. Helens
Volcanoes have been erupting and causing destruction for centuries, all over the world. The most dramatic eruption for Americans was that of Mount St. Helens, in Washington State. Because it happened relatively recently, many people can still remember when the mountain “blew” on May 18, 1980.
At 8:30 in the morning an earthquake occurred under the mountain, causing an enormous landslide on the north slope. As rock and ice hurled down the mountainside at speeds of 70 to 150 miles per hour, the superheated water and gases inside the mountain burst forth in a huge blast. Within six minutes, the blast had leveled 3.2 billion board feet of prime forest over an area of more than 150 square miles. That is enough lumber to build 640,000 houses. Much of the debris of the landslide fell into Spirit Lake, causing waves up to 850 feet high. While some of the snow at the top of the mountain was changed into steam immediately, much of it melted and produced mudslides that destroyed 27 bridges, 200 homes, 185 miles of roadway, and 15 miles of railway.
By the end of the nine-hour eruption, Mount St. Helens was 1,314 feet shorter than it had been on May 17th. This eruption proved that catastrophic events can change the landscape dramatically in a short amount of time, though normal erosion processes are slow.
Watch the Mount St. Helens video for more information on the eruption and its effects!
Does it ever give up? Italy’s Stromboli, an island volcano on the Mediterranean Sea, has been erupting almost constantly for about 2,000 years.
Biggest volcano on earth? Mauna Loa, in Hawaii, is the largest volcano in the world, as well as one of the most active. It has a height of 13,680 feet above sea level and covers an area of 2,035 square miles; it occupies about 50% of the largest Hawaiian island. Mauna Loa has erupted 33 times since its first recorded eruption in 1843. Cotopaxi, in Ecuador, is taller — about 19,300 feet above sea level — but does not cover as great a portion of land.
Lava longevity? Did you know that the volcanic ash spewed out by a volcano is easily eroded? Once it is gone, it leaves behind the central tube of lava that cooled inside the mountain. Devil’s Tower in Wyoming is believed to be an example of this phenomenon. Go to this site to see pictures of the Tower: http://www.ohranger.com/devils-tower/photos
The Scientific Speaker
Volcano: This word comes from the Latin Volcanus, which is the name of the Roman god of fire, whom we call “Vulcan” in English.
Guyot: A drowned volcanic island.
Laze: A hydrochloric acid mist formed by the action of lava on seawater.