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Fins of Fire Earthcache EarthCache

Hidden : 1/15/2012
Difficulty:
1.5 out of 5
Terrain:
1 out of 5

Size: Size:   not chosen (not chosen)

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Geocache Description:


That portion of the earth’s surface known as the Big Bend has often been described as a geologist’s paradise. In part this is due to the sparse vegetation of the region, which allows the various strata to be easily observed and studied. It is also due to the complex geologic history of the area, presenting a challenge to students and researchers from all over the world.

Not all field geologists, however, refer to the Big Bend as a paradise. For some, this land of twisted, tortured rock is a nightmare. The abundance, diversity and complexity of visible rock outcrops is staggering, especially to first-time observers. From 500 million year old rocks at Persimmon Gap to modern-day windblown sand dunes at Boquillas Canyon, geologic formations in Big Bend demonstrate amazingly diverse depositional styles over a vast interval of time.

The spines of dark rock you see marching along the desert floor here are called dikes.


These outcroppings are evidence of the most recent igneous activity in the area. Like great stone fences, dikes can be traced for miles across the park. They resemble spikes on the back of a Triceratops. They are reminders of the molten world beneath the quiet desert surface.

Dikes are tabular or sheet-like bodies of magma that cut vertically or almost vertically through and across strata, though some dikes are steeply inclined. Hundreds of dikes can invade the cone and inner core of a volcano. Dikes may occur in swarms of parallel dikes, particularly where there has been crustal extension. In regions of crustal extension, fracturing may open the route for filling by magma from a deep source, or intrusive magma may promote the fracturing and extension of the crust. Outcrops of dikes can range from a few metres to many kilometres in length, and can spread lateral distances from a few centimetres wide to over 100 m. Very thin dikes or dikelets are sometimes called veins.


Most dikes are made of magma, but sediments can form dikes too. The sandstone dike was emplaced as hydrocarbons and gases moved into the thick sand bed soon after it was buried, and the sand dike rose into the overlying mud while all of the material was not yet hardened into stone. Igneous dikes are common in many bodies of plutonic or highly metamorphosed rock, where molten or fluid materials have invaded preexisting rock formations. What defines a dike is that it cuts across the bedding planes of the rock it intrudes. When an intrusion cuts along the bedding planes, it is called a sill. In a simple set of flat-lying rock beds, dikes are vertical and sills are horizontal.

To claim credit for this cache, answer the following questions...
1. What do you think is beneath the surface here?
2. According to the sign, how long ago were these dikes created?
3. How do you think the spike-like formations were created?
4. Bonus points for pictures although this is not mandatory.
Park superintendent Bill Wellman is aware of the creation of this earthcache.

Additional Hints (No hints available.)