By Edwin Schiele
October 21, 1998. Today we finished our tour of the south flank. Early in the morning, ARGO II passed over a large crater. A series of depressions surrounded the crater. We took a closer look at these depressions and concluded that they were lava channels.
One of the things we wanted to determine was whether the lava that flowed through these channels was moving towards the crater or away from it. If we found that the lava flowed towards the crater and into it, we would conclude that the crater was not the site of a primary eruption. Instead the lava would had to have erupted elsewhere. If we found that the lava flowed from the crater, it would be less clear whether the crater was formed from a primary vent or secondary flow feature.
First we had to see if we could find remnants of lava flows in the channels. We were successful. One of the channels had a sheet flow on top of the rubble. A far more difficult task is determining which direction the lava flowed. Here is one method. Think of a crowd of people running down a long hallway. The people running down the middle of the hallway have the clearest path, so they run the fastest. The people running along the edges of the hall, however, continually scrape against the walls. The constant bumping slows these runners down. Battered and bruised, they eventually collapse from exhaustion. When lava flows through a channel, the lava at the edges scrapes up against the side of the channel and slows down, cools off, and begins to crust over. The lava flowing down the center of the channel has a clearer path, so it moves faster. Now try an experiment. Place a piece of cloth on a table and put a weight on the right edge. Then push the left edge of the cloth forward. You will see wrinkles forming that point in the direction you are pushing the cloth. If you pull the cloth back towards you, the wrinkles will point in the other direction. These same wrinkles form along the edges of the lava flowing through the channel. By seeing which direction these wrinkles point, it is possible to determine the direction the lava was moving. We will be looking over the videos of this lava flow for signs of wrinkles.
Pillows, sheets, rubble, and other forms of lava are not the only objects of interest on Puna Ridge. There are fascinating creatures able to withstand the intense pressure thousands of meters deep. In some areas, we have seen groups of brittle stars splayed out over lobes of pillow lava, and small, feathery tube worms (not the large kind found on hydrothermal vents) poking out of their burrows like little Christmas trees. We have seen fish and shrimp-like creatures swimming by. One time I saw a ray lying in the sediment. Mark Bulmer reported seeing a shark during his watch. Then there are the strange blob creatures and lollypop creatures and the strange creepy spider-like things. Since I am the only person on board with a biology background, everybody expects me to know what these things are. Its true that I studied ecology, but I did all of my field work in the forests of Maine and northern Michigan. The animals that live in these forests are not the same as those that live 3,000 meters underwater off the coast of Hawaii. So Im not much help.
We can also watch dramas unfold just off the side of the ship. At night, the ship's lights attract flying fish and other small, edible animals. They in turn attract larger animals such as mahi mahi, shrimp and even dolphins that are looking for an easy meal. Matt Naiman, a DSL engineer and the navigator during my watch, wrote the following about what he observed.
Tonight I got off watch and went out on deck near a light illuminating the water over the starboard side. Found the squid were feeding on small fish near the surface. The squid circle around just at the shadow line then strike quickly. If the small fish get away, the squid quickly retreats into the shadows edge. They seem intelligent enough to capitalize on our light for feeding purposes. Reminds me of owls and bats at night working the street lights for bugs.