On To Day 22Return To Day 20Day 21. Volcanoes on Another World

By Edwin Schiele

October 6, 1998. This morning at 7:15, Kevin Johnson, Laura Kong, Tim Dulaney, Mike Avgerinos, and Mike Relander wearily entered the galley and silently ate their breakfast. They had just finished the 16th and final wax core. The wax core marathon had been a success. Most of the cores had yielded chunks of black, sparkling glass, an indication of relatively recent eruptions. Much more analysis will come later.

Argo Launch (L. Dolby)
ARGO II takes the plunge!

At 1:30, we crowded onto the deck to watch the DSL group and crew launch ARGO II. The crane lifted the 6,000 pound vehicle, and the crew used ropes to guide it off the back deck and into the water. A rocking ship can transform a three ton object suspended from a long cable into a nasty pendulum that could seriously damage both the vehicle and anything in its way.

The first line will take ARGO over a terrace adjacent to the ridge crest, then up the steep slope to the summit. We will be watching for the sources of the lava flows that may have created these terraces. We are also watching for lava tubes and skylights looking into these tubes. If these features are present, they may serve as a preview of what we will be seeing further down the south flank and at the end of the ridge. For a discussion on the south flank and how terraces may form, see days 10, 15, and 17 of the daily flashes.

This cruise has brought together many scientists who bring with them a wide range of interests and talents. From now until the end of the cruise, we will occasionally feature one of these scientists.

Many people are interested in studying Puna Ridge because it can provide insights into the dynamics of other volcanoes around the world. Mark Bulmer is here to gain insights into the dynamics of volcanoes in other worlds. While studying for his doctorate at University College in London, Mark became involved in the Magellan mission to Venus. Magellan was a spacecraft that orbited high above Venus’ hot dense atmosphere. Its mission was to map the planet’s surface in much the same way we are mapping Puna Ridge. Instead of bouncing sound waves off the surface like the DSL 120, Magellan used a synthetic aperture radar. Mark is continuing his research at the Smithsonian Institution in Washington, D.C.

Venus, which is roughly the size of Earth, has an atmosphere of carbon dioxide, a surface temperature that will melt lead, and a pressure that will crush anything that descends into it. Of particular interest to Mark and many other scientists studying Venus are the planet’s geological features. Volcanoes as small as one kilometer and as large as 4,000 kilometers cover its surface.

sonar image of a series of domes on Venus
A radar image showing a series of domes on Venus. The largest is 30 km in diameter. (Magellan NASA/JPL)

Mark has the same questions about the volcanoes on Venus as we have about the volcanoes on Earth. When did they form? How did they form? What are they made of? How are they changing over time?  Mark studied the radar images and was struck by volcanoes that formed round, smooth, symmetrical domes. He also saw examples of stellate or star-shaped volcanoes that were no longer round, but instead had extensions radiating out.

Mark wanted to determine why the shapes of these volcanoes changed from circular to stellate. Possible processes include different styles or types of eruptions, diking, and his preferred cause, slope failure (land slides).

The best way to test these theories is to travel to the volcano and collect samples. Obviously, collecting samples from Venus is not very practical. The next best approach is to find volcanoes on Earth that resemble those on Venus. Mark could then apply what he learned about the volcanoes on Earth to those on Venus. Mark searched on land, but found no volcanoes that had the same shape as those he saw on Venus.

Sonar image of an Hawaiian seamount
A sonar image of a stellate-shaped seamount on the SE Hawaiian Ridge. It has landslide material around the base. (GLORIA H1 USGS)

Then Mark saw some sonar data that reinvigorated his search. In the early nineties, a research cruise had used a sonar vehicle called GLORIA to map the seafloor around the Hawaiian Islands. The sonar images that GLORIA produced were similar in quality and resolution to the radar images of Venus. Mark examined these images and found both symmetrical and stellate volcanoes on the seafloor that resembled those on Venus. Mark then started examining the geological processes that may have formed these seafloor volcanoes. He found that many of these volcanoes have had slope failures and that the dynamics of these landslides on the seafloor appear to be similar to those that have have occurred on the domes on Venus. Some of the best examples of these big landslides can be found off the Hawaiian Islands.

Mark now has some terrestrial volcanoes on which to model the volcanoes he is seeing on Venus. By studying the DSL 120 sonar data, ARGO images, and core samples from Puna Ridge, he hopes to learn how the symmetrical volcanoes form, and what processes, such as diking and landslides, are responsible for creating the stellate shape.

Ship Tracks October 14 through October 16

Ship Track October 14-16
Blue = Days 14 and 15
Red = Day 16
Go back to day 20. Go to day 22