Lava Viscosity TestsViscosity is the resistance of a liquid to flowing. It can also be thought of as how thick a liquid is. For example, water flows much more easily than honey so water has a lower viscosity than honey.

Viscosity of MagmaAt the extremely high temperatures and pressures inside Earth, mantle rock sometimes mels to

form magma. Surprisingly, the properties of magma can vary. For example, not all magmas have the same viscosity. This viscosity of the magma depends on its silica content and its temperature.

*Locate the vials containing magma from the three test locations. Carefully turn each vial over and time how long it takes the air bubble to travel to the other end of the tube. Do this several times for each tube in order to determine which sample is the most viscous and which is the least. Record your observations in your data chart.

Honey has a

higher viscosity.

Water has a

lower viscosity.

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Volcano Shapes and Eruptions

Volcanic eruptions create landforms made of lava, ash, and other materials. These land forms include shield volcanoes, cinder cone volcanoes, and composite volcanoes among others.

*Look at the pictures of your 3 volcanoes and read their eruption histories. Then fill in the data on your chart for type of volcano and eruption style.

Eruption Styles

Quiet Eruptions – In a quiet eruption the gases trapped in the magma bubble out gently and the lava oozes quietly from the vent. It can flow for many kilometers. Quiet eruptions are common on shield volcanoes and help build the gradually sloping sides of these massive land features.

Explosive Eruptions – In an explosive eruption the magma does not always flow out of the crater. Instead, it builds up in the volcano’s pipe, plugging it like a cork in a bottle. Dissolved gasses trapped in the magma build up pressure until they explode. The erupting gasses and steam push magma out of the volcano with incredible force! A Pyroclastic flow occurs when an explosive eruption hurls out a mixture of hot gasses, ash, cinders, and bombs.

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Rocks and Silica ContentMagma is a complex mixture, but its major ingredient is silica. The compound silica (SiO2) is made up of particles of the elements oxygen and silicon. Silica is one of the most abundant materials in Earth’s crust. The silica content of magma ranges from about 50 percent to 70 percent.

The amount of silica in magma helps to determine its viscosity and the color of the igneous rocks that form. 

*Look at the rock samples that were collected from each volcano. Record the color of each rock sample as light, dark, or medium.

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Pictomicrographs

A pictomicrograph is a photograph or digital image taken through a microscope to show a magnified image of an item. Pictomicrographs if rocks can help determine the minerals present and in what amounts. Silica forms hexagonal crystals so the more hexagonal patterns present in the image the more silica.

* Examine the pictomicrographs for the rocks from each volcano. Record which rocks actually have the most silica and the least silica based on this evidence.

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