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How does a geyser geyse?
Subject
Science
Visual Arts

Objectives
The student will:
  • Supply the definition of a geyser with 100% accuracy.
  • Identify, verbally and in writing, the ingredients necessary to form a geyser with 100% accuracy.
  • Create a model of a geyser.
  • Hypothesize, in writing, which geyser model will most accurately represent a real geyser, based on the background information and class discussion.
  • Evaluate different geyser models for their performance simulation of a real geyser, based on the background information and class discussion.
  • Accept or reject hypothesis regarding which geyser model will most accurately represent a real geyser after viewing the eruption demonstrations.

Materials
Antacid tablets
Film canisters
Vinegar
Baking soda
Soda bottles
Clay
Straws
Plastic cups
Plastic Bowls
Funnels
Paper
Pencil
Geyser Worksheet and Observation Guide

Background
A geyser is a hot spring that erupts periodically and forcibly ejects water. Three ingredients are necessary for a geyser to exist: a source of heat, an abundant supply of water, and a special underground plumbing system.

Much of the water in Yellowstone’s geysers begins as rain or snow. The moisture seeps into the ground and then rises back up as it flows through the plumbing system of the feature. The round trip may take hundreds, or even thousands, of years. Faults, fissures, and cracks in the Earth provide paths in which the water passes. The narrow places, or constrictions, of a geyser’s plumbing system distinguish it from that of a hot spring.

Eventually, the water encounters rocks that have been heated by underlying areas of magma. This rocky stove warms the water to the point where it becomes so hot that it can dissolve the silica from the surrounding bedrock. When the water approaches the surface, it begins to cool. The silica drops out of solution and coats the geyser’s plumbing system. This coating makes the system strong enough to withstand tremendous pressure.

A geyser eruption is triggered when the superheated water fills the geyser’s plumbing system and the geyser begins to act like a pressure cooker. The boiling point of a liquid is dependent upon the pressure. The boiling point of pure water is 212°F (100° C) at sea level. In Yellowstone, where the elevation is about 7,500 feet (2,250 meters), pressure is lower, and the boiling point is 199° F (93°C). Within a geyser’s plumbing system, much of the water can reach temperatures greater than 400°F (205 °C) and still remain in a liquid state due to the great pressure exerted by overlying surface water and rock.

As more hot water continues to enter the geyser’s plumbing at depth, the water temperature climbs high enough to overcome the pressure. Some of the water converts to steam. As the steam bubbles become larger and more plentiful, they can no longer rise freely through the constrictions in the plumbing system. Temperatures build and the boiling becomes more turbulent. Eventually the violent bubbling forces some of the underlying water through the constriction. This release creates an instant reduction in pressure. Much of the water in the system flashes instantly into steam and forcibly ejects the remaining water.

The character and function of a geyser are determined by its plumbing system and every geyser is unique. In 1992 and 1993, a probe equipped with a video camera and temperature and pressure sensors was lowered into Old Faithful Geyser’s vent. At a depth of approximately 45 feet, the probe encountered a constriction that was barely four inches wide. Beyond this narrowing was an opening about the size of a large automobile.

Discussion Points for Students
What is a geyser? What natural ingredients form a geyser? How does a geyser erupt? How does a geyser’s plumbing system differ from that of a hot spring? Why are constrictions necessary in the plumbing of a geyser?

Procedure
The instructor will:
  1. Review the process and ingredients that make a geyser.
  2. Instruct students to write a definition for a geyser and to list the three natural ingredients necessary to form a geyser on the Geyser Worksheet and Observation Guide.
  3. Make a small hole in the lid of a plastic film canister with a ball point pen, needle, nail, or other small, sharp object.
  4. Select a student to assist with the demonstration in Step 3.
  5. Fill the film canister ¾ full with warm water. Then instruct the student to add a piece of an antacid tablet (approximately ½ tablet). The student should replace the punctured lid quickly and place a finger over the hole in the lid. Instruct the student to shake the canister a few times and then remove his/her finger from the hole. Instruct class to observe the ensuing eruption.
  6. Ask students to describe what happened and why.
  7. Divide the students into groups of 3-4 persons.
  8. Inform students they will be given approximately 15 minutes to assemble a geyser’s plumbing system and will have a variety of household items from which to choose (See the items listed under “Materials” for suggestions. Instructors may either collect the materials themselves or suggest items that each student should bring from home.)
  9. After the allotted time, instruct each group to explain why they chose to assemble their geyser in the manner they did.
  10. Ask students to hypothesize in writing which of the geyser models will most accurately represent a real geyser.
  11. Remind students that heat creates pressure in the Earth. In the classroom, pressure is being created by the chemical reaction of adding baking soda to vinegar.
  12. Instruct each group to demonstrate their geyser’s function by pouring ½ cup of vinegar into their geyser model and then adding ¼ cup of baking soda.
  13. Ask students to write their observations on the eruption of each geyser model on the Geyser Worksheet and Observation Guide.
  14. Instruct students to examine their observations and evaluate which geyser model most accurately represented a geyser. Based on their evaluations, they should then accept or reject their previous hypothesis.

Assessment
How Does a Geyser “Geyse”? Rubric

Resources
Bryan, T. Scott. 1995. The Geysers of Yellowstone. University Press of Colorado.



Post Trip Lession Plan
National Science Standards for Grades 5-8
NS.5-8.1 Science as inquiry
NS.5-8.2 Physical science
NS.5-8.4 Earth and space science

National Arts Education Standards for Grades 5-8
NA-VA.5-8.1 Understanding and applying media, techniques, and processes
NA-VA.5-8.2 Using knowledge of structure and functions
NA-VA.5-8.6 Making connections between visual arts and other disciplines


Partners
National Science Foundation logo. Visit the NSF website.
This material is based on work supported by the National Science Foundation under Grant No.0307709
Yellowstone Park Foundation logo. Visit the Foundation's website.
Funding for this trip was provided by generous grants to the Yellowstone Park Foundation.