Tabernacle Hill: Lava Tubes 🌋 EarthCache

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, use the info below, 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!

1. When did Tabernacle Hill and the nearby Pahvant Butte form, according to the given info?
2. Next, observe some of the nearby lava tubes, and the rock they are made from; then describe them in general. Note the texture, color, and formations of the stone here. Based on your observations, were there multiple eruption flows in these tubes, or no? Explain.
3. (Optional): Take and post a picture of yourself and / or the Lava Tubes in the online log.

Lava Tubes 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 Obsidian Fields found to the SW, and also Pahvant Butte, a dormant volcano to the NW which is a fun area to explore, especially the lace curtain formation on its north side. 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 the nearby Ice Springs aka the Cinders, another interesting sight found in the Black Rock Desert
(source: Utah Geologic Survey)

Intro to Tabernacle Hill

This gently sloping hill you find youself on is actually a dormant volcano, specifically a cinder cone volcano, and it hasn't been dormant too long (geologically speaking). In fact, about 15,000 years ago, this area was mostly underwater, in the middle of what we now call Lake Bonneville, an ice-age lake formed by the melting of immense glacial deposits across the Intermountain West. However, volcanic activity has been the norm here for millions of years, and about ~15,500 years ago, the nearby Pahvant Butte erupted up through the icy waters of the lake.

Around the same time frame, within several hundred years, its twin was born as well. Now known as Tabernacle Hill, this formation was so named because the local Mormon settlers thought it resembled the shape of the Mormon Tabernacle up in Salt Lake City. You can still see the crater of the old volcano nearby, just to the south of here from the lava tubes that flowed away from it.

Image: Here we stand at the edge of the Tabernacle Hill Crater, and to the north is seen Pahvant Butte in the distance, 15 miles away (source: Lee Siebert, Smithsonian Institute)

​Creation of Tabernacle Hill

While both Pahvant Butte and Tabernacle Hill are basically volvanic twins, they are not identical. Tabernacle Hill was created by balsatic magma that erupted here, rising out of the lakebed, and it became a cinder cone of material that was created as the magma surfaced, cooled, and intereacted with the waters of Lake Bonneville. This cone rose as lapilli or tuff (gritty, basaltic fragments of rock) and ash built up around the caldera, or crater of the volcano.

Later, the lava continued to flow, but now less explosively and as it did it left behind a basalt flow that flowed away from caldera / crater downwards towards the surrounding valley floor. This is when the lava tubes here began to be formed.

NOTE: THE CACHE LOCATION POINTS OUT ONE OF THE EASIER-TO-ACCESS TUBES 

Lava Tube Formation

Lava tubes in general are usually formed in the following manner. A river of basaltic lava erupts / flows out of the crater onto the surface along a pre-existing channel, following the natural contours in the landscape. As this lava stream gradually cools down from the outside in, a crust starts forming on top and at the sides. If the magma is hot enough it may even melt its way down, deepening the channel or going underground. If the sub-surface stream of molten lava then continues to flow unobstructed towards an outlet then it will leave behind the overgrown channel as a long, tube like cave.

Image: when lava tubes start out on the surface, they tend to form as diagramed above
(source: Bruce Rogers, United States Geologic Survey)

Existing lava tubes can then see multible rivers of magma flow through them, sometimes filling them, at other times remelting them and altering their interiors and pathways. into many different shapes and forms. This is why lava tubes can be multi-layered, both vertically and horizontally, and why their interior surface is highly varied in terms of formations and textures, ranging from jagged points and ridges, to silky smooth walls.

The evidence of multiple flows of lava is often evident in the form of layers of flow lines and ledges on the walls formed by successively shallower streams of lava flowing through the tube, sometimes leaving behind hardened lava falls where the magma has flowed down from one layer to the next.

Image: here are some examples of the different formations often found in lava tubes
(source: Ken Grimes)

The floors of lava tubes tend to be smooth, as is to be expected given the fact that they are essentially the surface of a river that eventually stopped flowing. However, the floors of lava tubes are often times covered with litter or rocks that have crumbled down from the roof of the cave. This happenes almost exclusively during the cooling phase of the lava that surrounds the tube as it cools from the top down resulting in the still flowing – albeit extremely slowly – lava moving at different speeds. Once the lava has fully hardened and the tube is stable it takes a lot to dislodge any part of the roof. This is not to say that lava tubes are immune to the movements of the crust created by, say, a major earthquake.

Traveling the Tubes

While the volcano that created these tubes has long been extinct, they are still dangerous places. Be sure to bring lots of water, as it is a dry and often hot climate here. The road is best traveled in a high clearance vehicle, and it is best to  Also, make sure you have adequate clothing: the sharp rocks, darkness and low ceilings can be dangerous. 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.