Manuka State Park - Pit Crater EarthCache
Manuka State Park - Pit Crater
-
Difficulty:
-
-
Terrain:
-
Size: 
(not chosen)
Please note Use of geocaching.com services is subject to the terms and conditions
in our disclaimer.
A pit crater (also called a subsidence crater or collapse crater) is a depression formed by a sinking or collapse of the surface lying above a void or empty chamber, rather than by the eruption of a volcano or lava vent. Pit craters are found on Mercury, Venus, Earth and Mars. as well as many of our solar systems terrestrial moons. Pit craters are often found in a series of aligned or offset chains and in these cases, the features is called a pit crater chain. Pit crater chains are distinguished from catenae or crater chains by their origin. When adjoining walls between pits in a pit crater chain collapse, they become troughs. In these cases, the craters may merge into a linear alignment and are commonly found along extensional structures such as fractures, fissures and graben. Pit craters usually lack an elevated rim as well as the ejecta deposits and lava flows that are associated with impact craters. Pit craters are characterized by vertical walls that are often full of fissures and vents. They usually have nearly circular openings.
As distinct from impact craters, these craters are not formed from the clashing of bodies or projectiles from space. Rather, they can be formed by a lava explosion from a bottled up volcano, (the explosion leaving a shallow caldera), or the ceiling over a void may not be solid enough to prevent the collapse of the overlying material. A pit crater also could result from the collapse of lava tubes, dike swarms, or from collapsed magma chambers under loose material.
A newly formed pit crater has steep overhanging sides and is shaped like a cone inside, growing wider closer to the bottom. Over time the overhangs fall in and the crater fills with talus from the collapsing sides and roof. A middle aged pit crater is cylindrical but the rim will continue to collapse, expanding outward until the crater resembles a funnel or drain, narrower at the bottom than the top.
While pit craters and calderas form from similar processes, the former term is usually reserved for smaller features of a mile or less in diameter. The term "pit crater" was coined by C. Wilkes in 1845 to describe craters along Hawaii's East Rift Zones.
Hawaii is known for its volcanoes and pit craters. In 1868 an eyewitness saw more than two-thirds of the basin of Kilauea cave in and fill with a lava lake. This process happened repeatedly. The modern Halema'uma'u Shield began growing and then collapsed into a deep funnel-shaped pit. This pit filled with lava and for 19 years burned continuously, becoming famous as the Hawaiian Fire Pit. In 1924 the lava lake emptied when the walls of the crater cracked and collapsed and filled with water that turned to steam. After a week and a half Halema'uma'u had widened and was 1,700 feet deep. Rocks that were blasted away from the crater can still be seen on the caldera floor.
There are three basic types of lava which can be seen in Hawaii:
- A'a lava: A rough type of lava building loose, broken and sharp surfaces.
- Pāhoehoe lava: This type is having a smooth, billowy, undulating, or ropy surface.
- Block lava: Is a kind of a'a lava but having bigger parts and is flowing more slowly than a'a.
This pit crater is on a 2-miles hiking trail in the Manuka State Park. Please use the parking coordinates, restrooms are available here.
Be aware of the information at the parc entrance.
To log the cache please send then answers of the following questions to the email adress: geocaching@thomas-kuehn.de
Pictures from you at the cache are welcome, but not needed for logging.
Q1. Regarding the description of a pit crater above: Please describe the difference of a pit crater to a caldera in your own words.
Q2. Have a look to the rim of the crater. What do you think how old the crater is? (young, middle-age or older)
Q3. Look around the area of the pit crater. What kind of lava do you see? (A'a or pahoehoe)
Take care and have a lot of fun when going to this earth cache.
References
Pit crater: Wikipedia
Lava types: Wikipedia
Additional Hints
(No hints available.)