# Converging Tectonic Plates Demonstration

Initial Publication Date: February 27, 2022 | Reviewed: August 4, 2022

#### Summary

During this demo, participants use springs and a map of the Pacific Northwest with GPS vectors to investigate the stresses and surface expression of subduction zones, specifically the Juan de Fuca plate diving beneath the North American plate.

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## Context

#### Audience

This demonstration can be used as part of any introductory earth science course to solidify and augment student understanding of convergent plate boundaries.

#### Skills and concepts that students must have mastered

Students should be familiar with plate subduction and convergence boundaries

#### How the activity is situated in the course

This demonstration can be used at any time in an earth science class, though is particularly useful when discussing plate tectonics, convergence boundaries, and the use of GPS to measure ground deformation. This demonstration is expected to take 5 - 15 minutes.

## Goals

#### Content/concepts goals for this activity

• The Earth is not always rigid.
• The Juan de Fuca and North American plates form a subduction zone in the Pacific Northwest where the Juan de Fuca plate moves beneath the North American plate.
• The Juan de Fuca and North American plates are "locked" at the plate boundary, causing the North American plate to be pushed and compressed inland.
• The land near the coast, closest to the plate boundary, crunches the most while farther inland, the land crunches less - similar to a spring.
• Scientists monitor motion of the land with GPS.
• During a large earthquake on the subduction zone, the western edge of the North American plate will spring westward.

## Teaching Notes and Tips

A complete video of this demonstration can be found on the UNAVCO YouTube Channel.

## Assessment

Ask learners to summarize their observations and to sketch the maps of before convergence and after convergence of the boundary. As an extension, have learners draw a velocity vector for each dot shown on the map.

The exercise includes sample questions the learner could answer. These can be used for formative assessment of understanding or they can be graded on a simple 2-point scale:

• 2 points = correct answer with thorough supporting evidence and/or complete description
• 1 point = answer not completely correct or lacking thorough supporting evidence or description
• 0 points = incorrect answer