Geologists rely on new technology more and more. Some new technology allows us to model the earth’s surface, like
the model you see in the Google Earth tool, and some describe the area below the earth’s surface!
Which method of investigation allows geophysicists to best “visualize” or model a buried magma chamber beneath a caldera or crater formed on the earth’s surface?
b. Seismic tomography
Deformation of the earth’s crust happens above a buried magma chamber.
Volcanos, fissures, craters, and calderas are all types of surface deformation.
As the magma chamber fills up, it expands like a balloon and pushes up on the ground surface. In response, the ground over the magma chamber stretches (again just like the rubber of a balloon!) and develops cracks.
Imagine two people are standing facing one another, and then a wide, broad crack in the earth’s surface grows between them. Imagine that crack is just like the crack shown by Kyle at 15 minutes in the video on Kilauea.
Do the two people on either side of this crack move closer together or further apart?
Hint: draw a picture to help you visualize this situation!
a. Neither, so the amount of crustal deformation is negligible
b. Closer together, so the deformation is due to compression of the crust.
c. Further apart, so the deformation is due to extension of the crust.
Often geologists use global positioning system (GPS) receivers fixed to earth’s surface to measure deformation. Unlike your smartphone, these particular GPS receivers are literally bolted to the ground.
The picture below is an example of a permanent GPS receiver:
Because the receiver is fixed to the ground, if one moves—then the ground itself moved! This change could indicate a few things, including tectonic plate motion, landsliding, or the bulging of a magma chamber!
Geologists can also pound 2 stakes into the ground, and then monitor their location during surveys.
It is useful to place 2 stakes or GPS receivers on either side of a volcano or an earthquake fault to monitor any crustal motion that occurs.
Which of the following events resulted in stretching of the crust such that the GPS receivers or markers move further apart?
a. Filling and swelling of the magma chamber below Pu’u O’o Crater on the island of Hawaii.
b. Any quiet period of inactivity between 2 earthquakes on the San Andreas fault.
c. Emptying and deflation of the magma chamber below Pu’u O’o Crater on the island of Hawaii.
d. A quiet period of inactivity for the Mt. Waialeale caldera on the island of Kauai.
A number of studies indicate periods of deformation on the floor of Yellowstone caldera and outside of the caldera. The total stretching or bulging over the past couple decades amounts to about 70 centimeters of swelling!
What process does this deformation most likely reflect?
a. Earth tides in northwestern Wyoming
b. Temperature changes due to solar radiation.
c. Magma filling the chamber buried below the floor of the caldera.
d. Magma leaving the chamber buried below the floor of the caldera.