The rocks, according to the Smithsonian Art inventory, used in the construction of this monument are called volcanic stone. Better known as basalt, it is one of the most common rocks on earth. Basalt mostly makes up the sea floor, but can be found on land near active and inactive volcanoes. Examples would be inside a solidified lava tube such of that in Hawaii or Iceland. Basalt Flows are formed from the solidification of lava flows. These are the youngest rocks in the world. Eventually, erosion takes place and breaks up the flows into basalt rocks. These are new rocks, but aren't the youngest.
Basalt is an igneous rock, meaning it was formed from the solidification of liquid magma. There are two types of basaltic rock: intrusive and extrusive. Intrusive basaltic rocks form usually inside or part of a volcano. This can happen inside the caldera or inside lava tubes. There are two types of ways Basalt can form. One is formed under water at divergent plate boundaries like the Mid-Ocean Ridge or at volcanic hot spots like Hawaii. The other way is that is flows out of a volcano on land such as that in the Cascades in the north western United States.
How do we tell the difference if it's formed on land or under water? By looking at the rock, we can classify them by observing the texture. If it formed under water, the basalt would have to cool extremely rapidly due to the cool air temperature. The rapid coolness of basalt flow makes it vesicular. Vesicular means that they contain vesicles or tube like structures. The were formed when bubbles inside the liquid magma were captured as the rock hardened. Extrusive rocks are generally lighter in weight due to the air it has trapped inside. It is also more course and uneven.
We can tell if a basalt rock was formed on land if it is smooth and less course. There is more of a pattern and regularity within the rock. The first basalt photo on this cache page best explains this. There are usually little to no vesicles present and it is much more dense since it contains little to no air bubbles. Although this can be not necessarily true. Erosion can take oceanic basalt rocks and smooth them out, giving us a misconception that they formed on land and that the ocean basin sunk. The only way to know for sure is to measure the rate of erosion to the relative age of the rock. We can do this by radioactive dating of the rocks.
Works Cited
http://www.wired.com/2011/04/geology-photo-contest/
https://flexiblelearning.auckland.ac.nz/rocks_minerals/rocks/basalt.html
http://www.pitt.edu/~cejones/GeoImages/2IgneousRocks/IgneousCompositions/3Basalt.html
TO LOG A FIND ON THIS CACHE YOU MUST GIVE ME THE CORECT ANSWERS. YOU CAN CONTACT ME THROUGH MY EMAIL OR THE GEOCACHING MESSAGE CENTER. ANY INCORRECT ANSWERS WILL RESULT IN A DELETED LOG
1. "Volcanic Flight" on the first line of your email AND list all geocaching names of your party so I can match your answers to them. Note, this IS cheating as only the person who sent their answers has learned something, while the others get a "free ride". It's not fair to others. If you all want to learn something, I would prefer each cacher send me individual emails in the spirt of earthcaching.
2. Take a photo of you (or your signature item if you don't want your face to be shown) with the BASALT around the plaque (NOT THE STATUE) in the background. Do NOT show any close up photos of the rocks around the plaque.This photo MUST be uploaded to your "found it" log. Please do not send any photos through the message center as Groundspeak compresses images. Each log MUST have a unique and different photo. No two logs may contain the same photo.
3. Describe the (a) texture, (b) relative size, (c) color(s) of the basalt here.
4. What are the similarities and differences among the individual basalt rocks?
5. Describe the weathering process of these rocks. Is there any rusting or corrosion? If so, where do you see it AND why is this occurring?
6. How many years has the rocks been exposed here? Has it been long enough for erosion to significantly deteriorate the rocks based on your answer above? Explain.
7. In your opinion, is the basalt used in this sculpture intrusive or extrusive? How can you tell?