A story to share together
Nadia's Paper Earth: Where Volcano Magma Really Starts
Nadia thinks magma flows up from Earth's core, until a scale model of the layers shows her that the crust is thinner than a pencil line and the mantle is solid rock. With an ice-and-salt test and a hot-water plume, she and Tomas work out where magma really forms and why it rises.
Page 1
Nadia's sixth-grade class was building one giant paper Earth, sliced open so everyone could see the layers inside. Her job, with her friend Tomas, was to show where volcanoes get their magma. Nadia grabbed a red marker and drew a thick tube from the glowing center straight up to a mountain on the surface. “Magma comes from the hot core,” she announced. Tomas tilted his head and asked how long that tube would really be.
Page 2
Nadia measured a string stretched from the center of the paper circle to its edge: thirty-two centimeters. Earth's real radius is about six thousand four hundred kilometers. “So every centimeter on our paper stands for two hundred kilometers,” she said, dividing in her head. That made the mantle about fourteen and a half centimeters thick on their circle. The liquid outer core came out at about eleven centimeters, and the solid inner core at about six.
Page 3
Then Nadia worked out the crust. Under the continents it is about thirty-five kilometers thick, which shrank to less than two millimeters on their circle. Her red tube would have to cross the whole mantle, nearly three thousand kilometers of solid rock that creeps only a few centimeters a year. Tomas brought over the class foam globe, where red pins marked the world's volcanoes. Most of the pins lined up along the painted cracks between tectonic plates.
Page 4
Nadia crossed out her tube. If magma forms near plate edges, something there must help solid rock melt. She remembered that where one plate slides beneath another, the sinking plate carries seawater down with it. Could water make hot rock melt more easily? Real mantle rock was impossible to bring to class, so she planned a stand-in test with two ice cubes from the same tray and a spoonful of salt.
Page 5
Nadia set an ice cube on each of two saucers and salted only the left one. The ice stood for mantle rock and the salt stood for the water carried down by the sinking plate. After ten minutes, the salted cube sat in a wide puddle while the other cube had only a thin film of water. “Salt lowered the melting point of the ice,” Tomas said. “Water could lower the melting point of hot rock in a similar way.”
Page 6
Next they needed to know why magma climbs upward through kilometers of rock. Tomas filled a tall glass jar with room-temperature water. Nadia filled a small bottle with cold water from the fridge, added red food coloring, and lowered the open bottle to the bottom of the jar. The red water slid out and spread across the floor of the jar like a puddle. “Cold water is denser, so it stays at the bottom,” Nadia said, frowning.
Page 7
Nadia rinsed the little bottle and refilled it with hot tap water and two drops of red coloring. This time, a red plume curled up out of the bottle and spread across the top of the jar. Warm water takes up a little more space than the same amount of cool water, so it is less dense and floats upward. Magma rises in a similar way, because melted rock is less dense than the solid rock around it.
Page 8
The crust was too thin to paint details on, so they cut a long paper panel to show a close-up of only the top two hundred kilometers. On it, Nadia painted an ocean plate sliding beneath a continent at a gentle slope. About a hundred kilometers down, just above the sinking plate, she dabbed a red pocket of new magma. Tomas painted a crack rising from it to a magma chamber below a cone-shaped mountain.
Page 9
Nadia built the mountain in layers, because volcanoes beside sinking plates grow over many eruptions. She stacked thin sheets of gray clay for ash and strips of red clay for lava, one on top of another, into a steep cone. On the far end of the panel, Tomas added a second place where volcanoes form, where two ocean plates pull apart. There, rising mantle rock melts because the pressure squeezing it drops.
Page 10
On presentation day, classmates crowded around the paper Earth and the long close-up panel. One of them laid a pencil beside the crust and laughed, because the pencil was wider. Tomas lowered the bottle of hot red water into the jar once more. Nadia pointed from the rising red plume to the red pocket of magma on the panel, and the whole class leaned in as the color climbed toward the top.
