Lesson Plan

Magma Mash

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Grade Level:
Fourth Grade-Eighth Grade
Subject:
Chemistry, Earth Science, Geology, Volcanoes
Duration:
20-30 minutes
Group Size:
Up to 36
Setting:
classroom
Keywords:
andesite, chemical elements, continental crust, extrusive, granite, granodiorite, igneous, intrusive, lava, magma, magma chamber, mantle, mineral, obsidian, oceanic plate, plutonic, solidus, tephra, mount rainier, Mount Rainier National Park, Cascades Volcano Observatory

Overview

In an exploration of magma behavior, students role-play minerals that are cooling at different rates, and then examine rock samples. This lesson plan is part of the "Living with a Volcano in Your Backyard" curriculum, created through a partnership between Mount Rainier National Park and the US Geological Survey Cascades Volcano Observatory.

Objective(s)

Students will:
  • Recognize and record differences and similarities of rock samples with similar chemical compositions.
  • Hypothesize about methods of rock formation.
  • Understand the effect of cooling rates on the appearance of igneous rocks.

 

Background

Upward ho! - magma ascent
All igneous rocks originate underground in the molten state as magma. Magma is hot molten rock containing chemical elements from melted mantle rock and oceanic plate. It also contains dissolved gases such as water, carbon dioxide, and possibly a few crystals. Magma forms in the mantle where the subducted oceanic plate has sunk to great depths. At Mount Rainier, magma forms from rocks about eighty kilometers (fifty miles) below Earth's surface. Temperatures and pressures at such depths are sufficiently high to cause water within the oceanic plate to sweat into the mantle rock. The addition of water to hot mantle rocks causes rock to melt and form magma. This magma begins to rise because it is less dense than surrounding solid mantle rock.

Rock flows at great pressure and temperature
Rock flows like putty in this inhospitable environment of great pressure and temperature. Rock that surrounds rising magma deforms, allowing passage of the magma. This partially molten magma eventually rises to the base of the continental crust. The upper continental crust is more rigid than the mantle, so the magma must force its way upward through cracks or by melting surrounding crust rocks. The magma creeps upward like giant fingers. By the time magma reaches Earth's crustal rocks, its density often is comparable to that of the surrounding crustal rock. Here the ascent of magma ceases. This stagnant mass of magma forms a reservoir called a magma chamber. From here, magma may cool and solidify in place, or continue its ascent to erupt eventually onto Earth's surface through a volcano. Once magma reaches Earth's surface, it is known as lava.

What happens inside the magma chamber?
You made of heard the expression that "birds of a feather flock together". In a similar way, individual chemical elements combine and form distinct minerals. They bond to each other and form complex structures with specific chemical patterns or crystalline structures (see Graphic: "Elements to Rocks"). Individual minerals combine to form large masses as illustrated in this activity. Minerals often look like small cubes, spheres and many-faced crystals. The longer it takes for magma to cool, the more time is available for crystals to grow and become larger mineral grains. Eventually, magma cools and crystallizes completely and becomes solid rock. Most magma cools slowly enough that all the liquid is used to form minerals. Some magmas cool so fast that the liquid hardens into glass. The solidus is the temperature at which all liquid in the magma becomes completely crystalline.

Cooling rates of magma
Magma that cools slowly over thousands of years develops minerals throughout its entire mass. These minerals continue to grow larger until all liquid has changed to crystal. We call these igneous rocks intrusive, or plutonic, in commemoration of Pluto, the Greek god of the Underworld. Granite and granodiorite are common plutonic rocks. Some magma ascends through cracks and breaks through the surface during a volcanic eruption. The resulting extrusive rock, called lava, cools quickly, providing little or no time for chemical elements to group together and form minerals. Volcanic rocks form in this way. Minerals in some volcanic rocks can be so small they are difficult to identify without magnification. These miniature mineral grains form the background, groundmass, or matrix that creates the principal color of a rock. Magmas that cool before chemical elements bond to form minerals solidify to a glass. Obsidian is one example of a volcanic glass.

Materials

Graphics and student pages for use in the Magma Mash Lesson Plan activities.

Procedure

Assessment

As this activity progresses, pay attention to student's understanding of the effect of cooling rates on the appearance of igneous rocks. Note how students' thinking progresses from basic observations of appearance to the causes of appearance and how the causes are related to volcanic processes. Use students' results on Magma Mash student page to assess their ability to observe and record experimental results; use Rock Sample Observations student page to assess ability to apply the concepts to identifying the source of igneous rocks in the real world.

 

Park Connections

At Mount Rainier, magma forms from rocks about 80 kilometers below Earth's surface. This lesson plan explores how the minerals within the volcano are constantly changing.

 

Extensions

  • The Rock Candy Experiment
    Make rock candy to demonstrate how crystals develop in magma. To show how rapid cooling effects the development of crystals, spoon some of the hot candy mixture into cold water before dispensing the remainder into the container for cooling. The candy mixture that cooled quickly should show no crystal development, while the slowly cooled mixture will create rock candy crystals.
  • Rock and Mineral Classification
    This activity can be used as part of a unit on rocks and minerals or to prepare students for scientific observations during a planned visit to Mount Examine and interpret five Native American stories about geologic events at Mount Rainier by making a storyboard.
    • Take students on a field trip to a local streambed to collect a variety of different rocks.
    • Instruct students to make up classification categories for the collected rocks. With a grid on the floor or on a large sheet of paper, ask students to arrange the rocks into different categories based on the classification system they developed. Afterwards, instruct students to arrange the rocks using the rock classification system commonly used by geologists.
  • Shoe Classification
    Students learn about classification systems by sorting shoes. Each student takes off one shoe and places it in a pile with their classmates’ shoes. Students then define categories to sort the shoes into different piles (smelly versus non-smelly, white versus. other colors, big versus. little, etc.). Once the shoes are sorted, they make up subcategories to sort them even more. Continue to do this until each shoe has been sorted into its own pile and can be identified as one particular person’s shoe. This is similar to how geologists sort rocks into categories and eventually identify the rock and give it a name.
  • Rock Stories
    Ask students to write a creative story illustrating the formation of a rock from magma to a solid.

Additional Resources

Francis, P., and Oppenheimer, C., 2003, Volcanoes: Oxford University Press, 536 p.

 

Harris, S. L., 2005, Fire Mountains of the west: the Cascade and Mono Lake Volcanoes: Mountain Press Publishing Company, 3rd edition, 454 p.