To log this Earthcache, you will NOT be looking for a typical geocache container (in fact, there IS no container to find). Rather, to prove you were here and learned something you'll need to find the answers to the given questions (found below as well as at the end of this description), which you will then email me, the owner (this is the same process for ALL Earthcaches).
So go ahead and log your experience while here, submit photos, etc., but email your answers to me (not in your visit log) to get credit for "finding" this cache. If it seems too complicated, don't sweat it too much (as long as I can see that you made an honest effort to answer all of the questions, that is fine). Remember that the purpose of this is to learn something, and most importantly, to have fun! Also, feel free to email me with any questions you may have, I'd be happy to help.
Special thanks goes to Teresa Frampton, the Outdoor Rec Planner at the BLM office in Fillmore, who generously gave permission for this earthcache to be created and placed.
To log this cache, head to the cache coordinates, or one of the given waypoints, and use the info above, your surroundings, observations and logic to answer the following questions. Email me the appropriate answers (don't post them in your log, or per Earthcache guidelines your post will have to be deleted), and most of all, have fun!
- When did the Cudahy Mine pumice form, according to the given info? What other rocks can form from the same molten lava?
- Next, observe the nearby pumice deposits, and where it is found; describe the pumice examples you find in general. Note the texture, color, and formations of the pumice & the surrounding stone here.
Lastly, pick one (1) of the following options, and answer the questions:
- Based on your observations, was this pumice formed from layers of pumice ash / "pumicite" that rained down over consecutive eruptions, or from a single large event? In other words, is it best described as pumicite, or pumice? Look at the vesicles for clues. Explain your answer.
OR
- Take some sample(s) of the pumice you find. Head to the nearby Black Spring Waypoint, and then test in the water tank if your sample(s) float(s). Explain what happens, and why this is:
OPTIONAL:
- If you wish, take and post a picture of yourself at the site(s) and / or some of the pumice you found in your online log. This is NOT a requirement, but it is fun!
Pumice in the Black Rock Desert
This area, known as the Black Rock Desert (volcanic field) was once a hotbed for volcanic activity, as other nearby sites indicate. This volcanic field covers over 2,700 square miles, from as far away as Topaz Mountain (with its interesting rhyolite deposits containing topaz and red beryl) to the Lava Tubes and Pahvant Butte, found to the NE of this location. Closest however are the Obsidian Beds that are found super close to here. Some of these formations were created ~15,000 years ago, while the most recent, such as the Cinders, erupted just 600 years ago!
Image: Here is a photo of several pressure ridges found near Tabernacle Hill, another interesting sight found in the Black Rock Desert (source: www.geology.utah.gov)
Intro to the Cudahy Mine & Deposits
Approximately 2.5 million years ago (late Tertiary Period), volcanic eruptions in the Black Spring area of the Black Rock Desert here in western Utah spewed out many different volcanic rocks, including granite, rhyolite, pumice, and obsidian. At this site, you will find some rhyolite, as well as obsidian, in addition to the plentiful pumice. Snowflake obsidian, a rare black obsidian with whitish-gray spots (spherulites) of radiating needle-shaped cristobalite (high-temperature quartz) crystals, can also found nearby here. Obsidian has been used for arrowheads and primitive cutting tools, and is presently used for jewelry.
Image: Here are a few examples of pumice, such as you might find at this site (source: www.sandatlas.com)
This particular deposit of pumice is found as part of a larger frothy rhyolite lava flow that occurred as part of the Pliocene Age (about 2.2-2.6 MYA). The mine (on BLM land) began sometime in the 1950s, but has not been in commercial operation since the 1970s. No one knows exactly how much more pumice may remain underground here, but it remains a great site to check out pumice in its natural state.
What Exactly is Pumice?
Pumice is a light-colored, extremely porous igneous rock that forms during explosive volcanic eruptions. It is often used in making lightweight concrete, as landscaping material, and as an abrasive in a variety of industrial and consumer products. Many specimens have a high enough porosity that they can float on water until they slowly become waterlogged.
Creation of Pumice
The pore spaces (known as vesicles) in pumice are a clue as to how it forms. The vesicles are actually gas bubbles that were trapped in the rock during the rapid cooling of a gas-rich frothy magma. The material cooled so quickly that atoms in the melt were not able to arrange themselves into a crystalline structure. Thus, pumice is an amorphous volcanic glass known as a "mineraloid."
Some magmas contain several percent dissolved gas by weight while they are under pressure. Consider that for a moment. Gas weighs very little at Earth's surface, but these magmas under pressure can contain several percent gas by weight held in solution. This is similar to the large amount of dissolved carbon dioxide in a sealed bottle of carbonated beverage such as beer or soda. If you shake the container, then immediately open the bottle, the sudden release of pressure allows the gas to come out of solution, and the beverage erupts from the container in a frothy mess.
Above: Pumice is formed in a process that resembles when a highly pressurized soba bottle is opened. Frothy magma is expelled (like frothy soda), and it quickly cools, trapping small air bubbles / vesicles inside the rock (source: www.dinojim.com)
A rising body of magma, supercharged with dissolved gas under pressure, behaves in a similar way. As the magma breaks through Earth's surface, the sudden pressure drop causes the gas to come out of solution. This is what produces the enormous rush of high-pressure gas from the vent. This rush of gas from the vent shreds the magma and blows it out as a molten froth. The froth rapidly solidifies as it flies through the air and falls back to Earth as pieces of pumice. The largest volcanic eruptions can eject many cubic kilometers of material. This material can range in size from tiny dust particles to large blocks of pumice the size of a house.
Large eruptions can blanket the landscape around the volcano with over 100 meters of pumice and launch dust and ash high into the atmosphere. The abundant vesicles in pumice and the thin walls between them give the rock a very low specific gravity. It typically has a specific gravity of less than one, giving the rock an ability to float on water.
Image: Even underwater volcanoes, when the pressure bursts the magma out, will form pumice. Here is some from a recent undersea eruption, floating due to its low specific gravity (source: geology.com)
Large amounts of pumice produced by some island and subsea eruptions will float on the surface and be pushed about by the winds. The pumice can float for long periods of time - sometimes years - before it finally becomes waterlogged and sinks. Large masses of floating pumice are known as "pumice rafts." They are large enough to be tracked by satellites and are a hazard to ships that sail through them (see image above; source: geology.com).
Forms: Pumice vs. Pumicite
Pumice is produced in two forms: rock pumice and pumicite. "Pumicite" is a name given to very fine-grained pumice (having vesicles measuring less than 4 millimeters in diameter down to submillimeter sizes). The word can be used synonymously with "volcanic ash." Sometimes, pumice can form from multiple eruptions, and it will appear in layers, as layer upon layer collects one on top of the other. Sometimes all of the pumice will be uniform in color, and this usually indicates that it was created in one large, single eruption event. Pumicite, the finer, often layered material, is usually mined from these volcanic ash deposits, or it can be artificially produced by crushing rock pumice.
Traveling the Black Desert
While the volcanic activity that created this pumice many years ago has long been extinct, the Black Rock Desert is still dangerous places. Be sure to bring lots of water, as it is a dry and often hot climate here. The roads are best traveled in a high clearance vehicle, and it is best to make sure you have adequate clothing: be careful of the sharp rocks, and please be respectful of the land, and practice Leave No Trace, as this is a BLM Area of Critical Environmental Concern, so that future generations can appreciate and enjoy this area just as you can.
Sources: adapted from various sources / websites, including geology.utah.gov, the U.S. Geological Survey, geology.com or as otherwise noted.
In conclusion, remember:
To log this cache, head to the cache coordinates, or one of the given waypoints, and use the info above, your surroundings, observations and logic to answer the following questions. Email me the appropriate answers (don't post them in your log, or per Earthcache guidelines your post will have to be deleted), and most of all, have fun!
- When did the Cudahy Mine pumice form, according to the given info? What other rocks can form from the same molten lava?
- Next, observe the nearby pumice deposits, and where it is found; describe the pumice examples you find in general. Note the texture, color, and formations of the pumice & the surrounding stone here.
Lastly, pick one (1) of the following options, and answer the questions:
- Based on your observations, was this pumice formed from layers of pumice ash / "pumicite" that rained down over consecutive eruptions, or from a single large event? In other words, is it best described as pumicite, or pumice? Look at the vesicles for clues. Explain your answer.
OR
- Take some sample(s) of the pumice you find. Head to the nearby Black Spring Waypoint, and then test in the water tank if your sample(s) float(s). Explain what happens, and why this is:
OPTIONAL:
- If you wish, take and post a picture of yourself at the site(s) and / or some of the pumice you found in your online log. This is NOT a requirement, but it is fun!
This cache was created by an
