Introduction
Ka'ū Desert is located on the south flank of Kilauea Volcano. Although it is within the boundaries of the National Park, it is free to enter. A well maintained trail leads past numerous interpretive signs highlighting both history and geology. The trail ends at a pavilion which displays fossilized human footprints dating back to the 1700's. Ample parking is available at the trailhead. At the GZ you will find a gigantic "accretionary lava ball" and an interactive display. This Earth Cache is intended to educate you on the formation of this interesting volcanic phenomenon.
Climate
Technically, Ka'ū Desert is not a true desert because it's rainfall can exceed 39 inches per year. However, acid rain is produced when precipitation combines with sulfur dioxide emitted from the nearby volcano. This rain, which can have a pH as low as 3.4, significantly stunts the growth of plant life in the area. Also, because the ground is composed of tephra (rock fragments and particles ejected by a volcano), it is extremely porous and subject to rapid evaporation. These natural features combine to produce a sandy, desert-like environment.
History
The eruption of Kilauea that occurred in 1790 is considered one of the most devastating in Hawaiian history. An enormous volume of volcanic ash was released at the very moment that Chief Keōua Kuahu'ula, his warriors, and their families were traversing this area. They were returning home to Kā'u after a battle with Chief Kamehameha when the ash caused at least 80 Hawaiian warriors and countless others to die from suffocation. Some of their footprints were preserved in the ash and are still visible today.
Lava Bombs
In the aftermath of a volcanic eruption, it is common to see spherical masses of solidified lava. These lava bombs form during explosive volcanic eruptions when semi-liquid or plastic magma is ejected from the vent due to the buildup of gas pressure. The bombs cool and solidify as they travel through the air before landing on the ground. They are most often found close to the volcano, however bombs from the most explosive of eruptions have been known to land as far as 3 miles (5 km) away!
Accretionary Lava Balls
Accretionary lava balls are NOT lava bombs! They form instead when a small fragment of solidified lava rolls along the surface of a liquid flow and lava sticks or "accretes" to its surface. The growth of a lava ball is similar to the way a giant snowball grows when soft, sticky snow adheres to its surface as it rolls downslope. Accretionary lava balls are roughly spherical masses that usually form on the surface of an `a`a flow and range in size from a few centimeters to several meters in diameter. They have the potential to be transported for tens of miles by these flows.
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In order to gain credit for this Earth Cache you must message me with the answers to the following questions. If I do not receive your answers, your log will be deleted.
1. Please estimate the diameter of the lava sphere at the GZ.
2. Describe the appearance/structure of the lava sphere.
3. Based on your observations of the structure and location from point of origin of this sphere, how do you know it's an accretionary ball and not a lava bomb?
4. If this lava sphere WAS a lava bomb, which volcano would it most likely have erupted from? Please explain how you reached your conclusion.
REFERENCES
Ka'ū Desert - Wikipedia
https://en.m.wikipedia.org/wiki/Ka%CA%BB%C5%AB_Desert
Volcanic Bombs - Universe Today
https://www.universetoday.com/39642/volcanic-bombs/
Volcanic Bomb | Properties, Formation, Composition
https://geologyscience.com/rocks/volcanic-bomb/?amp
Accretionary Lava Balls
https://volcanoes.usgs.gov/images/pglossary/LavaBall.php
Lava flows destroy everything in their path
https://www.usgs.gov/programs/VHP/lava-flows-destroy-everything-their-path