By Edwin Schiele
October 18, 1998. Its a time of little sleep and of long days in the control van watching the video monitors. At 7:30 last night, the vigil paid off. ARGO II had just come over the top of a large cone on the crest of the ridge and was exploring the lip of the crater. According to the sonar data, this is the largest cone on the ridge and resembles the cones on the subaerial portion of Kilauea. The other domes on the ridge have either flat or collapsed tops and more gradual slopes.
The video cameras focused in on rectangular columns of lava that are one to two meters long. These structures, called columnar jointed basalt, form from large thick flows. As these flows cool, cracks develop that are perpendicular to the direction that the flow is moving. Over time, the flow breaks up into these columnar pieces. So at one time, a large, thick lava flow poured out of this cone. This discovery excited everybody in the van.
Earlier in the day, ARGO II toured some fissures. During the last day of the sonar mapping, we had found a series of five parallel fissures that were interrupted by blobs of lava. Based on these sonar images, it appeared the lava had erupted from the fissures at various intervals. (See day 19 of the daily flashes.) It is common for eruptions to become localized along a fissure. For example, the current eruption on the subaerial portion of Kilauea started over a long stretch of a fissure, then confined itself to the Puu Oo crater. In Iceland, localized eruptions along fissures build into cones. We are interested in whether a similar process occurred on Puna Ridge.
First, however, we must determine the origin of these blobs of lava. Did the lava really erupt from the fissures, or did it erupt elsewhere then flow into the fissures. To find out, we needed to look at the contact points where the edges of these lava mounds meet the fissures. By examining the edges of these mounds, we can hopefully determine whether the lava flowed into or out of the fissures.
ARGO II first made a pass over all five fissures, then looped around. Just as Luke Skywalker daringly sped his spacecraft through the canyons of the Death Star, flyer Jim Varnum guided ARGO II down into one of the fissures. Of course ARGO II only traveled at a speed of one-quarter knot, and there was nobody shooting at it. The exhilarating joy ride ended after just a few minutes. A giant pile of pillow lava blocked the fissure, and Jim had to pull ARGO II out. We will have to wait until we analyze the video and photographs before we can determine the flow direction to see whether the lava blocking the fissure had originated from the fissure or from elsewhere. We also went over the top of a large, broad hill that we are for now calling "the pancake." At the summit, there is a mound that has a crack or fissure running down the middle. We are interested in how this mound may have formed. We are investigating two possibilities. Pressure from magma welling up underneath could have caused the summit to inflate. These bulges, called tumuli, are common on land, including on the subaerial portion of Kilauea. Only a few examples, however, have been found on the sea floor. The other possibility is that the mound was built from lava that had erupted from the fissure.
ARGO II found and traced the fissure. At some places, the fissure was five meters wide and 12 meters deep. It was filled with dark rocksa sign that an eruption had happened relatively recently. Pillow lavas cover the top of the mound. The lava flattened out towards the edges of the mound. The farther we moved from the mound, the older the lava got. Such a pattern suggests that the mound is constructional, but once again we will have to study the videos and photographs more closely before we can draw any definitive conclusions.
During the last few flashes I neglected to mention the arrival of scientists Denny Geist and Terry Naumann, teacher Naidah Gamurot, and the return of ship technician Rob Hagg. We also said goodbye to Hawaii school administrators Bob Golden and Larry Gaddis. The captain insisted on a larger shuttle, and the transfer of passengers proceeded flawlessly. The departure of Bob and Larry threw the ping pong tournament into chaos, since both had advanced into the later rounds. The bookies and backroom dealers are meeting to decide the outcome. On a brighter note, the new arrivals brought large bags of chocolate and several newspapers, including a Sunday Boston Globe for the many New Englanders on board. The chocolate lasted less than two days.