Sandwiches and volcanoesBy Queena N. Lee-Chua
Philippine Daily Inquirer
My student, Shela Bacuño, who teaches science to sixth graders at Uno High School, uses hands-on activities to help her students learn geology.
Ask students to cut out the seven continents from their world map then fit them together like a jigsaw puzzle. Glue the pieces on one or two bond papers.
Do the continents fit to form a single land mass? They do.
The single landmass from which the continents came is called Pangaea (“all lands”). Alfred Wegener proposed the continental drift or plate tectonics theory that stated that the continents were once a single landmass.
Why did the continents drift apart? Geologist Harry Hess suggested sea-floor spreading. Because the sea floor moves and often splits, cracks appear along the middle of ocean ridges.
Magma (a molten substance from the mantle of the earth) rises from the cracks and hardens, forming a new crust.
To illustrate this theory, get a biscuit sandwich. Break into two the top biscuit of the sandwich. Place the pieces back on top of the filling then slowly pull them apart. Press the sandwich until the filling oozes onto the surface.
Ask students what the biscuit and the filling represent.
Another theory suggests that convection currents flowing between the crust and upper mantle may be causing tectonic plates to move. Convection currents transfer heat through liquid or gas. Some parts of the mantle can flow like thick liquid, bearing tectonic plates with them. Imagine a dead bug being carried on a treadmill.
To illustrate convection currents, break a biscuit into four pieces. Place each piece on separate bond papers, making sure that the broken pieces still fit together even if they are on different sheets. Move the papers away from each other.
Ask students what the biscuit pieces and the bond papers represent.
Afterwards, give students common situations and ask them which theory each reminds them of:
A full toothpaste tube is squeezed. (sea-floor spreading theory)
Apple filling oozes out of a pie. (sea-floor spreading theory)
Boats move along a river (convection current theory)
Chicken pieces move in a pot of boiling water. (convection current theory)
A bracelet made up of beads breaks. (continental drift theory)
The pieces of a jigsaw puzzle are scattered. (continental drift theory)
Volcanoes are openings in the earth’s crust through which steam, ash and magma are released. Magma comes from deep inside earth. Because the mantle can grow extremely hot, pressure causes magma to push up to the surface through cracks in rock, causing volcanic vents to unplug and eruptions to occur. Magma released by a volcano is called lava, which eventually cools and hardens into rock.
To demonstrate a volcanic eruption, uncap a soda bottle. Use a potato or cork stopper as cap, holding it in place while shaking the soda bottle. Observe.
Warning: When shaking the bottle, make sure it is not pointed at anyone, especially during release.
The soda in the bottle represents magma. The potato stopper represents the hardened plug of magma. Pressure inside the bottle ejects the stopper. This is how a volcanic vent is unplugged and the volcano erupts.
“My previous students said, if volcanoes were so destructive, why not cover all the vents?” says Bacuño. “With their help, I created this story: You have superpowers and want to play hero during a volcanic eruption. With your great strength, you lift a huge rock and cover the erupting volcano. What do you think will happen next?”
Elicit discussion from students. Help them realize that if volcanic vents are plugged, more pressure is exerted that may cause an even more violent explosion.
Earthquakes are simply movements of the earth’s crust. They often occur along faults (cracks along the crust between tectonic plates). Earthquakes originate from a point underground called the focus. Plate collisions and volcanic eruptions can cause earthquakes.
The point directly above the focus is the epicenter. Areas near the epicenter are damaged most severely in a quake. Knowing the epicenter helps scientists figure out where danger is greatest, so lives can be saved.
Geologists use the seismograph to measure the strength of earthquakes, calculated using the Richter scale. An earthquake that registers 3.5 on the Richter scale is strong enough to be noticed. A 6.0 or higher can damage buildings.
To demonstrate how a seismograph works, attach a ballpoint marker to one end of a string. Tie the other end to an iron ring attached to a stand. The tip of the marker should reach the flat surface of a desk. Put a piece of paper just under the tip of the marker. Ask a student to shake the desk while another slowly pulls the paper toward himself or herself.
Afterwards, discuss what to do before, during and after an earthquake, like having an emergency plan at home and in school; storing supplies such as flashlight, battery-operated radio, extra batteries, first-aid kit, food, water, clothes; and securing heavy furniture or appliances to the floor or wall.
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