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2010 Guatamalan Sinkhole

30
skips
70
questions

Act One

• Robert Kaplinsky

March 08, 2013

How much material will they need to fill the sinkhole?

• Teacher note
In 2010, an enormous sinkhole (pictured below) suddenly appeared in the middle of a Guatemalan neighborhood and destroying a three-story building above it.
• 1.

What is a guess that is too low?

• 2.

What is a guess that is too high?

• 3.

• 4.

What information do we need to know to figure this out?

Act Two

• Teacher note
The first thing a person should think when they see this photo is â€œThere is no way this is real!â€ or â€œThis is totally PhotoShopped!â€ That is what makes the photo so amazing because it is completely real and documented by many reputable sources such as National Geographic, Time Magazine, and CNN. Each of these articles can explain why and how the sinkhole (technically called a â€œpiping pseudokarstâ€œ) happened better than I can, so I will focus on the math involved.
One of the sinkholeâ€™s amazing properties is how incredibly cylindrical it is. The other thing I find striking is how deep it appears. It looks like it goes down and never stops. I wouldnâ€™t be surprised if students thought it might go all the way through the Earth and come out on the other side (which apparently is not China but actually in the middle of the Indian Ocean). In actuality it does stop and this video below shows that better.
• Video2010 Guatemala Sinkhole
• Teacher note
All the challenges revolve around knowing the sinkholeâ€™s dimensions, however its reported dimensions vary. You can have students discuss the three reported options and debate to find the one that is most reasonable or skip this step and go with CNN article I have included (which I believe has the most accurate dimensions):
National Geographic: â€œ60 feet (18 meters) wide and about 30 stories deepâ€ (assuming a story is about 10 feet, then about 300 feet deep)
Time Magazine: â€œruns some 200 ft. deepâ€
Slate: â€œA sinkhole, 65 feet across and 100 feet deepâ€
I think it is worth having students reflect on how reasonable these estimates are. Here are some of my thoughts:
National Geographic, CNN, and Slate seem to agree that the diameter is about 20 meters, so that is what I will assume.
The depth measurement varies from 100 feet to 200 feet to 300 feet. Obviously that is a huge difference.
The pictures donâ€™t seem to be helpful in determining the depth.
Looking at the video, the sinkhole looks to be a little more than 1.5 times deeper than it is wide. So, that seems to match up with the CNN and Slate measurements.
Going forward with dimensions of diameter of 66 feet and depth of 100 feet, we can use the formula for the volume of a cylinder: pi * radius^2 * height. That gives us pi * 33^2 & 100 cubic feet or approximately 342,119.45 cubic feet.
Interestingly, Slate appears to have made a mathematical error in their reporting (below)
• Teacher note
The only way I see how they could get 6,500 cubic feet as an answer using their reported dimensions of 65 feet in diameter and 100 feet in depth is to multiply 65 by 100. Clearly that is not correct. This is a great opportunity for students to double check the validity of their answer and defend their reasoning.
Update: I actually contacted the articleâ€™s author and he replied â€œApparently you picked the wrong article for a math lesson! I apologize. It appears you are correct.â€ So, it is an example of how even professionals make silly mistakes and how we have to check our work to make sure it is reasonable. Using low, high, and best guesses is helpful for this.
The next challenge is â€œHow much will it cost to fill the sinkhole in?â€. Obviously a lot of assumptions need to be made. Slate reported that in 2007 Guatemala filled a larger sinkhole (about 330 feet deep) with concrete. So, using that information:
A cubic foot of concrete currently costs about \$4. \$4 * 342,119.45 costs about \$1,368,477.80. That obviously does not include labor, material transportation, or really anything besides the concrete itself. The price of concrete also varies, so it would be reasonable for the total cost to be somewhere between \$1 and \$2 million. In the Slate example, the previous sinkhole cost \$2.7 million so this seems like a reasonable estimate.
• ImageView of the sinkhole with the helicopterâ€™s shadow in the hole.
• ImageClose view of the sinkhole
• ImageClose view of the sinkhole
• ImageClose view of the sinkhole