Volcanoes: Explosive and Effusive

Name:

Homeroom:

Background Knowledge: Volcanic eruptions may be explosive (violent) or effusive (passive), depending on the lava chemistry (amounts of silica and dissolved gases). Silica is a mineral found in nature as sand or quartz. High levels of silica mean very viscous (thick) lava, and low levels mean more fluid lava. Dissolved gases like sulfur dioxide, water vapor, and carbon dioxide build up inside the volcano, similar to how carbon dioxide builds up inside a can of soda that has been shaken. The higher the level of gas, the more pressure that builds – and the more violent an explosion. The combination of silica and dissolved gas levels determine the type of eruption and shape of the volcano. Volcanoes are classified by their shape and lava chemistry.

My Notes of the Background Information:

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Lava Viscosity:

Not all volcanoes have the same type of lava. Some volcanoes are viscous, meaning that they are thick and sticky, while other volcanoes have thin, runny lava.

We will test out the viscosity of various substances and see how they relate to lava flow.

Procedure:

1)Stack 3 books on top of the lab station. Place one end of a cardboard on it so it slopes into the aluminum pan.

2)Mark a “Start” line and a “Finish” line.

3)Pour substances down the ramp and time how long it takes to get to the Finish line. Record the data below.

Substance / Time / Viscosity is… because…

Mt. St. Helens is a volcano that has explosive eruptions, while Hawaii has volcano eruptions that are not explosive. Which substances are similar to the lava chemistry (viscosity) of Mt. St. Helens and which ones are similar to Hawaii? Explain using data from your experiment.

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Dissolved Gases:

Gases trapped inside magma build up pressure inside the magma chamber, much like shaking a container of soda or other carbonated beverage. Some volcanoes have more gas in their magma than other volcanoes. Which amount do you think would yield an explosive volcano, more or less dissolved gas? (Think back to shaking a carbonated beverage.)

Prediction:

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The Upcoming Simulation Requires Safety Glasses:

1)You will be given two alka seltzer tablets. Break one in half. Set one half off to the side. Break the other half in half. You should now have one full tablet, ½ tablet, and two ¼ tablets.

2)With your film canister, pour 20mL of water in.

3)MR. SHUTES IS SERIOUS ABOUT WEARING SAFETY GOGGLES.

4)Drop one of the ¼ alka seltzer pieces into the canister and close the cap immediately.

5)Let it sit for more than 2 minutes. Observe the canister. (Are bubbles forming? Is the cap beginning to swell up?)

6)Empty the contents of the canister. Pour 20mL of water in. Place ½ tablet and close the cap off immediately. Observe the canister.

7)Empty the contents. We will now see what happens when the top of a volcano allows for some degassing. We will do this by leaving the cap partially off when we conduct this portion of the experiment.

8)Pour 20mL of water in the canister. Place ¼ of a tablet in to the canister and place the lid on partially. Observe what happens.

9)With the remainder of the alka seltzer, come up with other variables to test to see how explosive volcanoes can be.

Data Collection:

Amount of Alka Seltzer / Observation
1/4
½
¼ with lid partially off

What Do You Think?

How would you rank the explosivity of these four combinations:

1)High viscosity with a lot of dissolved gas

2)High viscosity with a small amount of dissolved gas

3)Low viscosity with a lot of dissolved gas

4)Low viscosity with a small amount of dissolved gas.

(Please answer with the most explosive and then to the most effusive. Answers should include a claim, evidence from your lab data, as well as reasoning from real world examples like Mt. St. Helens and Hawaii.)

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Modified From:

Issue 9: Earth’s Changing Surface (December 2008)

Re-modified Mr. Shutes 2014