Background: YOU MUST READ the BACKGROUND INFORMATION BEFORE YOU BEGIN!

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Volcanic Eruption Lab

Objective: I will simulate the relationship between the mineral composition of lava and its viscosity. I will demonstrate the relationship between the viscosity of lava and its explosive character during an eruption.

Background: YOU MUST READ THE BACKGROUND INFORMATION BEFORE YOU BEGIN!

Viscosity: the resistance of a fluid to flow. Fluids with a high viscosity resist flow. This is the typical response in explosive eruption styles (e.g. Mount St. Helens). Fluids with a low viscosity flow freely, typical in more effusive eruption styles (e.g. Hawaiian or Icelandic shield volcanoes or the Columbia River flood basalts).

Explosive character – how explosive a volcanic eruption is. Since we are creating a model, and not observing a real volcano, we will measure explosive character by how much “lava” is ejected from the magma chamber of our volcanos.

·  Effusive Eruptions: where lava flows like a thick, sticky liquid up to weeks at a time. In effusive eruptions, degassing is common but ash is usually not.

·  Explosive Eruptions: where fragmented lava explodes out of a vent over a short and infrequent period of time. In explosive eruptions, the fragmented rock is often accompanied by large amounts of ash and gases that are suspended into the atmosphere.

Types of Lava/Magma

The three common types of lava—basaltic, andesitic, and rhyolitic—contain different amounts of silica (SiO2) and dissolved gases. They have different viscosities based on the amount of silica they contain. Low-silica lavas are less viscous and travel faster than higher-silica lavas, which are more viscous and travel slower. Viscous lavas sometimes cool before they travel very far, which is why they are often less hazardous. When magma or lava cools and solidifies, it forms igneous rock. (Basalt, andesite, and rhyolite are all igneous rocks.) The following chart lists common lava types and their flow rates. Note that lava flows pass through a range of viscosities as they cool and solidify; as lava loses heat, its viscosity increases.

Only ten elements make up the bulk of most magmas: oxygen (O), silicon (Si), aluminum (Al), iron (Fe), magnesium (Mg), titanium (Ti) calcium (Ca), sodium (Na), potassium (K), and phosphorous (P). Because oxygen and silicon are by far the two most abundant elements in magma, it is convenient to describe the different magma types in terms of theirsilicacontent (SiO2). The magma types vary frommafic magmas, which have relatively low silica and high Fe and Mg contents, tofelsic magmas, which have relatively high silica and low Fe and Mg contents.

Problem: What kind of lava (high, medium or low viscosity) do you think will result in the most explosive volcanic eruptions?

Hypothesis:

If ______

then, ______

because ______.

Set-up - Create your lava:

Materials:

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·  Flour (representing felsic minerals)

·  Water (representing mafic minerals)

·  3 large beakers

·  Food coloring – red, blue & green

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Procedure:

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1.  In one of the beakers, make lava that is 2/3rd felsic minerals and 1/3rd mafic minerals. Stir until smooth. Color this lava with red food coloring.

2.  In a second beaker, make lava that is ½ felsic minerals and ½ mafic minerals. Stir until smooth. Color this lava with blue food coloring.

3.  In the third beaker, make lava that is 1/3rd felsic minerals and 2/3rd mafic minerals. Stir until smooth. Color this lava with green food coloring.

Part I: Flow Rate

Materials for Part I

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·  Tray

·  Plastic wrap or aluminum foil

·  Marker

·  Lava from set-up

·  3 spoons

·  Stop watch (may use cell phones)

·  Ruler

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Procedure:

1.  Set up a ramp at your table using the tray. Cover the tray with plastic wrap or aluminum foil to keep it from getting dirty and to make clean up easier. (Extend the plastic wrap or aluminum foil past the book onto the table in case something runs off the tray.)

2.  Near the top of your ramp, mark 3 separate starting lines with a marker.

3.  Collect a tablespoon of each type of lava. (In your data table, label these lavas by their mineral composition as well as their color.)

4.  Plop one of the lava samples down at the top of the ramp at one of your start lines.

5.  Get out a stopwatch and allow the lava to flow down the ramp for 2 minutes.

6.  Measure the distance the lava has flowed from the start line to its current location in centimeters (you may want to mark the point with your marker to make measuring easier).

7.  Calculate the flow rate of the lava by dividing the distance it traveled by the time it took to travel that distance.

8.  Repeat steps 4-7 for the other two lava types.

9.  Clean up your tables.

10. Based on the flow rates you found, include a column in your table for viscosity. Rate each lava as having either a high, medium, and low viscosity (refer to the definition of viscosity up top).

Part II: Explosive Character

Materials for Part II

Name______Date______

·  lava from set-up

·  newspaper

·  baking powder

·  vinegar

·  three 50 mL beakers

·  three 50 mL Erlenmeyer flasks

·  spatula

·  3 droppers

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Procedure:

1.  Cover half of your table with at least 2 layers of newspaper.

2.  Measure 3 separate samples of baking powder, each weighing 15 g.

3.  In each of the 3 small Erlenmeyer flasks, pour one of the 15g samples of baking powder. Shake the flasks to flatten out the layer of baking powder.

4.  Fill each 50 mL beaker with one of the lava types and bring them back to your table. (In your data table, label these lavas by their mineral composition as well as their color)

5.  In each Erlenmeyer flask, fill it to the brim with each of the types of lava, covering the baking powder. When filled, each flask will contain about 60 mL of lava. (it will take some time and patience to pack the high viscosity lava into the flask, assign one person from your group to work on this while other tasks are completed).

6.  Fill 3 droppers with as much acetic acid (vinegar) as you can (equal amounts in each dropper).

7.  Each dropper can hold 10 mL of fluid so estimate how much vinegar you are using and record.

8.  Place one of your volcanoes on the newspaper and insert a dropper filled with vinegar into the bottom of the volcano.

9.  When ready, squeeze the dropper to release the vinegar into the baking soda, causing the production of carbon dioxide gas. Observe the volcanic eruption.

10. DON’T REMOVE THE DROPPER UNTIL THE REACTION IS OVER.

11. Measure the amount of lava ejected from the volcano by observing what lava remains in the Erlenmeyer flask and subtracting that from the original amount.

12. Repeat steps 8-11 for the other two lava types.

13. Clean up your table. If anything seeped through the newspaper, wipe it up!

14. Based on the amount of lava ejected from each volcano, include a column in your table for explosive character. Rate each volcano as having either a low, medium, or high explosive character (refer to our definition of explosive character up top).

Rubric

Extension

Mount Nyiragongo is a volcano in the Democratic Republic of the Congo, 18 kilometers from Goma near the Rwandan border. The area surrounding the mountain is highly populated. The volcano has very fluid basaltic lava with an unusually low silica content. The lava moves extremely fast. During the 1977 eruption, the initial speed of the lava flow was estimated at 100 kilometers per hour. When Nyiragongo erupted in January 2002, more than 250,000 people were temporarily displaced when the lava, flowing at speeds of about 60 kilometers per hour, overran the town of Goma.

1.  Nyiragongo is said to have lava that flows "like water." Based on your investigation, describe the viscosity of the lava produced by Nyiragongo.

2.  How might the viscosity of lava from a volcanic eruption affect the outcome of an evacuation?