Download Activity 2 Modelling Convection Currents

Teacher Resource
Experiential Science 30—Freshwater Systems
Activity 2 Modelling Convection Currents
Time
• 1 class period
Activity Type
• lab
• chapter project
• research team
S T U D E N T B O O K P. 36
Materials and Equipment
• Each research team needs: Bunsen burner or alcohol lamp; straw or glass tube, approximately 150 mm long × 3 mm internal diameter; ring stand; water; potassium permanganate (VII) crystals (KMnO4); 600 mL heat-resistant glass beaker; video camera
Teaching Suggestions
• If materials for this activity are not available, there are other ways to model convection
currents. Instead of using potassium permanganate, for example, place ice cubes made
from water heavily dyed with blue food colouring into warm water.
• Although it is preferable for students to experience the convection current firsthand,
there are demonstration videos on the internet (use “convection current video” as a
search term to find examples).
• For an open response activity, have research teams design their own models to demonstrate convection currents. Be prepared to discuss modifications or other ideas. You
might provide students with a list of materials, for example, some of those listed for
this activity: the beaker, glass tube, Bunsen burner, ring stand, water, and potassium
permanganate. Or you might bring alternative materials into the classroom. You might
invite each group to perform their demonstrations and have a class discussion about
what worked and what did not.
• After completing this activity, brainstorm how convection currents are apparent in
students’ everyday lives (for example, cloud formation, winds, ocean currents, water
boiling in a kettle).
• This is an opportunity to discuss with students how simple models can help scientists better understand more complex issues. Discuss with students how this
activity can be used to help explain the processes of plate tectonics. Encourage
students to put their understanding of plate tectonics into their own words.
Procedure—Expected Results
4. The potassium permanganate will start to dissolve right away and turn the water purple at the bottom of the beaker. As the contents are heated, purple water will rise to the
surface creating a purple vertical column of fluid, move along the surface horizontally
where it will cool, and sink, thereby modelling convection currents on a small scale.
When the heated beaker is viewed from the side, and the potassium permanganate is
situated at the side of the beaker, the current will flow along the top of the water’s surface in one direction, away from the heat source.
5. When the heated beaker is viewed from the side, and the potassium permanganate is
situated in the centre of the beaker, the current will flow along the top of the water’s
surface in two directions, away from the heat source towards both sides.
Chapter 1 Plate Tectonics and Volcanoes
Reflections and Conclusions—Suggested Answers
1. The coloured water in both cases follows a circular path. The path rises from the heat
source towards the surface, moves along the surface, then descends as it cools, eventually flowing towards the heat source to replace the water that was rising. The only
difference is that, in step 5, the heat source in the centre creates a convection current
on either side of the heat source.
2. Answers will vary, but should summarize the relationship as follows. The Earth’s giant
internal convection current is the driving force of plate tectonics. The less dense,
hot magma rises towards the surface where it travels laterally and cools, becoming
more viscous and dense, and then sinks, continuing the cyclical process. The friction
between the convecting magma and crust causes the plates to travel and collide with
other plates, creating geologic features such as mountains and volcanoes.
3. Answers will vary, but this model supports the theory of plate tectonics because the
path of the coloured water is such that the hot, coloured water rises up from the bottom—just as magma does. At the top of the beaker, the coloured water moves horizontally along the surface—just as magma, cooled at the surface, is carried by the
convection current along the surface of the Earth. The coloured water at the top cools
and then sinks, because the cooler water is denser, just as portions of the Earth’s crust
descend below other plates. Essentially, the movement of the coloured water follows
the same general pattern as the Earth’s crust, only on a much smaller scale. This is crucial because the giant internal convection current in the mantle has enough energy to
move whole continents, making mountains and valleys, and divide oceans.
4. Make sure that students store their videos for inclusion in their chapter projects.
EVIDENCE OF PLATE TECTONICS
S TUDE NT B O O K P P. 3 7 – 4 4
• To introduce this section and assess prior knowledge and experiences:
§§ Ask your class open-ended questions such as: What evidence of geologic activity have you seen or experienced? and What stories have you heard from Elders
regarding earthquakes?
§§ Provide mapped examples of geologic activity in the Northwest Territories to help
prompt responses and invite the class to write down possible explanations for why
earthquakes occur in specific areas. At the end of the section or chapter, have students review and revise these explanations, based on what they have since learned.
• Students may find it useful to make a list or table of the evidence for the theory of plate
tectonics that includes the resulting geologic activity (earthquakes, volcanic eruptions, geothermal activity), lateral continuity of rock strata, and sea-floor spreading.
Encourage them to add subheadings and examples, notes in point form, and graphic
organizers.
• To capture students’ interest, post a map of Earth’s tectonic plates on a wall and have
them consider the relationship between plate boundaries and earthquakes, volcanoes,
and geothermal activity.
Case Study­—Oral Accounts and Art Point to an Earthquake
S TUDE NT B O O K P. 3 8
• Discuss how oral tradition has supplied scientific evidence for earthquakes and
tsunamis.
Teacher Resource
Experiential Science 30—Freshwater Systems
• This is an opportunity for students to reflect on Traditional Ecological Knowledge and
how geologic processes may have affected peoples in the past.
• Encourage students to share local stories or narratives of indigenous peoples from
around the world about how they survived earthquakes and tsunamis.