Snorkeling in a Volcano (Molokini) EarthCache
Snorkeling in a Volcano (Molokini)
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Mahalo for visiting Maui, the island where I was born. To complete this earth cache, you must take a charter/tour boat to the Island of Molokini from Maalea Harbor. There is light snorkeling involved, so understand the risks with the tour (you will probably have to sign a waiver of some sort).
”Swimming in a Volcano Crater of Molokini”
The tiny, crescent-shaped island of Molokini lies 3 miles offshore of Haleakala volcano, East Maui. Molokini is a volcanic cone that rises about 500 ft from the submarine flank of Haleakala. The cone is capped by a crater, although the northern rim is below sea level and the crater is flooded by the sea. The crater area of the cinder cone is commonly referred to as a "lagoon".
Molokini would be similar to cinder cones elsewhere along the southwest rift zone except that it erupted through water. When magma erupts explosively in shallow water, the liquid water heats, expands rapidly, and changes to steam, adding to the eruptive force. The extra force shatters the extruded lava, which exposes more hot material--and hence more steam and more force as the eruption grows. Near-shore eruptions are some of the most dangerous that Hawaiian volcanoes can produce.
Shallow marine eruptions have two consequences for the appearance of the resulting cone. The first is grain size, because the ripping power of these marine eruptions leads to finer-grained deposits than in cinder cones onshore. The second is the abundance of volcanic glass, because the lava fragments are quickly cooled by water before crystals can form. Glass is a geologically unstable material. A cinder is a pyroclastic material. Cinders are extrusive igneous rocks. Cinders are similar to pumice, which has so many cavities and is such low-density that it can float on water. For those dying to know, the Molokini deposits are basanite, a type of basalt with fairly low amounts of silicon and high concentrations of sodium and potassium. (Geochemists would say it contains 45 percent SiO2, 4.4 percent Na2O, and 1.4 percent K2O.) Visible crystals are sparse, even under a magnifying glass.
As you snorkel off of your tour boat, you will see much coral and marine life below the ocean level. Coral coverage in this area can reach over 70% of available hard substratum. Boulder, sand and coral habitats are present. Water quality is essentially oceanic in nature, with high transparency and low nutrients.
To get credit, please upload the picture and email me the following:
1. Take a picture of you with the GPS before getting in the water (don’t take the GPS with you snorkeling), and upload it to this log entry. If you can bring a disposable underwater camera, take some pictures of the reef with the inhabitants. Please DO NOT touch the reef or take any of it with you.
2. Cinder eruptions on land tend to be reddish and black in color. Lava fragments quickly cooled by water mentioned above create “glass like” rock material of a different color. What color does most of Molokini or the edges seem to be?
3. What is your estimate of the diameter of this crater if the entire rim was above water? When snorkeling, how deep do you estimate the bottom of the crater being?
4. Extra Credit: After taking some pictures or viewing the coral. Email me the scientific or common name of most of the coral present here.
Additional Hints
(Decrypt)
Gnxr n gbhe obng, mbqvnp, fnvyobng, be nal bs gur znl gbhef.
Qba'g jbeel vs V qba'g rznvy onpx nf V trg gbaf bs rznvyf. Rawbl naljnlf.
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