37°42'54"N 119°40'36"W
Magmatic features:
Enclaves
Let's learn about enclaves!
Similarly to dikes, enclaves can be seen all over Yosemite. In the image to the right, you can see two enclaves that look like dark grey shapes in the rock.
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What are enclaves (on-kleiv)?
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Enclaves are volumes of rock surrounded by a host rock of a similar, but different composition. This is why, in the image, the enclaves have a different color than the surrounding rock.
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We can get a better understanding of how this occurs by doing an activity!
37°48'24"N 119°32'43"W
activity: oil and water
Let's do an activity together! If you would like, you can do this activity at home, or you can participate virtually!
Supplies
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two cups (preferably see-through)
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oil
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water
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red food coloring (for fun!)
Directions​
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Pour the oil into one clear cup and the water into the other. The amount of oil should approximately 1/4 to the amount of water.
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Add a few drops of red food coloring to the water (to make it look like magma)
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Pour the oil into the water and stir. Do they mix together?
Magma 1
Magma 2
Now that we have our supplies, let's see what happens when these two magmas mix!
No matter how much you try to stir the liquids together, they simply will not mix. This causes bubbles of oil to form in the water. Why does this happen?
Oil and water will not mix due to their different viscosities.
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What is viscosity?
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Viscosity refers to a material's resistance to flow. For example, honey has a high viscosity because if you were to try to pour honey down a slope, it would travel slowly. However, water has a low viscosity because it would travel quickly.
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When magma bodies of different compositions meet underground, they sometimes have different viscosities and cannot fully mix. Similar to minerals, magma compositions can be referred to as felsic or mafic. Felsic magmas have a high viscosity, while mafic magmas have a low viscosity.
The enclaves that we see in these images show that a mafic magma mixed with our felsic host magma. The mafic magma could not mix and the magmas cooled to form these rocks.
Compare these two images.
37°48'39"N 119°29'06"W
If we were to freeze the video from the activity, we would see the enclaves of oil in the water. When magmas mix, they sometimes cool and preserve the enclaves so we can see them in the rock, like the image above.
Hopefully, now you have a better understanding of what an enclave is and how it forms!