Teacher Logbook:
Friday, July 14, 2000 1600 hrs.

Today we're diving in an area called ASHES. The superheated fluids flowing from the ASHES vent field receive their heat from a magma chamber about 2 km below Axial. The chamber and Axial owe their existence to the fire within our planet that geologists have only recently come to understand. They must infer the process occurring in Earth's interior through seismic (earthquake) waves and the surface expressions, or features that compose the crust of the Earth. Inference into these processes is not a recent pursuit. Throughout history many have attempted to explain such questions as why there are continents scattered throughout our global ocean. Through a range of geological studies people worked toward a better understanding of the Earth but it wasn't until the 20th century that the various disciplines of geology were tied together.

In 1912 a scientist named Alfred Wegener proposed a theory for some observations he, and others made. A map of the Atlantic Ocean shows Africa and South America as two pieces of a jigsaw puzzle pulled apart. He stated, citing fossil and glacial evidence, that these two continents were once together. In fact all the contintents were connected at one time as a giant supercontinent surrounded by an ocean. This landmass, Pangaea, split up about 200,000,000 years ago and the continents drifted to their current positions where they continue to drift today. Most geologists at the time rejected this radical idea of continental drift. In 1940 Hugo Benioff used seismic data to plot earthquake and volcanic activity on a map. He found a pattern of activity around the Pacific Ocean now known as the Pacific Ring of Fire. Later, studies of what we now know as oceanic ridges were conducted. It was found that oceanic plates are born along these ridges and become older as one moves away from either side of a ridge. The seafloor spreading theory was born. Later still, subduction zones were described as regions where plates were destroyed as they descended into Earth's interior.

Finally, in 1965 J. Tuzo Wilson combined continental drift and seafloor spreading into the most powerful concept that geologists use today. Termed plate tectonics, this theory states that Earth's outer layer consists of about a dozen separate plates that float on a layer below them. With heat-driven movement from the Earth's interior the gigantic plates are dragged, and over millions of years they may move significant distances. Most of the million or so earthquakes and volcanic events each year occur along the boundaries between these plates. Axial Volcano, along the Juan de Fuca Ridge, is at the boundary of the Pacific Plate and the Juan de Fuca plate. Here, oceanic crust is born. It will travel some 250 miles and then descend below the North American plate. As a result of this subduction process, the Coast Ranges of Oregon and Washington, the Olympics, and Cascades Mountains were created. Therefore, plate tectonics ties Axial Volcano to the volcanoes of the Pacific Northwest: St. Helens, Rainier, Hood, Shasta, etc.

Jeff

Mushroom Vent in the ASHES vent field.

Hell Vent at ASHES.

Sulfide worms under Pork Chop, a flange of Hell Vent.