LAVA TUBES
Lava typically travels in channels away from the point of eruption. As the molten lava flows, the rock beneath the lava flow heats and can melt, while the surface of the molten lava tends to cool. Many times the top of the channel will cool enough to completely harden, while the lava continues to flow through this “tube” beneath the surface. Thus, a lava tube in born.
When the lava flow at the start of the tube stops or is diverted elsewhere, the remaining lava in the now non-active tube may partially drain from the tube, leaving behind a lava tube cave. The resulting caves can be over 50 feet high or wide, and can continue underground for miles. The Kazumura Lava Tube Cave, located south of Hilo, is over 40 miles long and includes multiple lava falls and cascades. The walls and ceilings of lava tubes are typically rounded and are fairly consistent in diameter. Inside the lava tubes you can frequently find stalactites (aka lavacicles) and stalagmites, formed by molten lava dripping from the ceiling of the lava tube. One of the easiest access lava tubes on Hawaii is the Thurston Lava Tube located in Volcanoes National Park.
SEA CAVES
Sea caves, or littoral caves as they are also called, are formed primarily by the erosion of rock by wind and waves. Wind and waves in general would erode a shore evenly. However, faults or weak zones in the rock erode more quickly and are the starting point for the sea cave formation. As the rock continues to erode, the cave will enlarge in both length and width, and frequently height, as the rock overhead loses support and falls in. Eventually the interior cave ceiling may fall, leaving the cave entrance as a remaining structure – essentially forming a sea arch. Further erosion of the arch ultimately results in the failure of the arch, leaving just the stump of the arch remaining as depicted below:
While sea caves can form in sedimentary, metamorphic, or igneous rock, those formed in igneous rock tend to be larger. This is due to the greater strength of igneous rocks. Some of the largest sea caves in the world are located along the Na Pali coast of Kauai. The Waiahuakua sea cave there extends 1,155 feet in length, with a separate entrance and exit formed by the joining of separate sea caves. This sea cave is the second largest in the world.
Sea Caves tend to be small in length, with a recent survey of sea-caves revealing only 25 caves worldwide longer than 200 meters in length. Compared to lava tubes, sea caves will also have a much more irregular shape (due to erosion), and will open up in width past the cave entrance, due to the concentration of the wave power in a confined area. Sea cave walls tend to be irregular and chunky, indicative of the erosion process where the rock is broken piece by piece from the cave wall. Lava tube walls are smoother in general, and sometimes contain horizontal ledges, indicating the level of the lava flowing within the tube. Sea caves can also be hundreds of feet wide, compared to the relatively narrow width of lava tubes (typically less than 60 feet).
THE CACHE
As you will have noticed, this cache is a terrain 5 – it is only accessible by water. The difficulty is also high, as the distance from the ramp to the final location and back is nearly 5 miles. It is recommend that you bring a waterproof GPS unit to direct you to your destination, as you will very likely get wet during this adventure.
To log this EarthCache, you will need to venture to three waypoints. At each waypoint you will need to determine the following information and email us the answers:
- Do you think this location is a lava tube, sea cave, or stump? What evidence is there at the location to support your conclusion?
- For lava tubes or sea caves, what are the approximate height, width and depth of the opening?
In addition, you need to post a photo of you or a personal item with one of three waypoints in the background.
Logs that fail to include this requirement will be deleted.
DISCLAIMERS: Remember – you are pursuing this geocache at your own risk This cache is not for everyone. You need to be in good physical condition to paddle 5 miles round trip to approach this cache. Make sure you respect the weather and water conditions and don’t pursue this EarthCache when conditions are not safe or favorable. We recommend you DO NOT ATTEMPT THIS CACHE ALONE. PLEASE DO NOT KAYAK INTO THE WHITE WATER ALONG THE SHORE OR IN THE CAVES. Be sure to bring along at least one partner for safety reasons. Please use your best judgment in deciding whether to tackle this difficult cache. It is highly recommended you bring at least one liter of water with you for hydration. No one is forcing you to seek this cache. If you choose to seek this cache, you do so only of your own free will and fully and totally on your own responsibility.
BIBLIOGRAPHY
UNDERSTANDING LAVA TUBES AND LAVA CAVES - Harry Shick ISBN: 978-0-9853350-0-7
Volcanic Landforms and Surface Features – Jack Green, Nicholas M Short. Springer-Verlag New York. Library of Congress Card no: 70-144791.
Chasing Lava – A Geologist’s Adventures at the Hawaii Volcano Observatory – Wendell A Duffield. Mountain Press Publishing Company
Sea Caves. Retrieved August 2, 2014 from http://en.wikipedia.org/wiki/Sea_cave
Lava Tubes. Retrieved August 2, 2014 from http://en.wikipedia.org/wiki/Lava_tubes
Lava Tubes and Caving. Retrieved August 18, 2014 from http://www.nps.gov/elma/naturescience/lava-tubes-and-caving.htm
Coastal Landforms 101 Sea Caves, Arches, Stacks and stumps. Retrieved August 1, 2014 from Wikispaces: http://coastallandforms101 .wikispaces.com/Sea+Caves,+Arches,+Stacks+and+stumps
Sea Caves. Retrieved August 1, 2014 from http://www.lilburnes.org/Students/Caves/sea_caves_ivanna.htm