Show Date: August 2, 2006 
Pam Eastlick for THE DEEP on line

WHERE IT GOES
AND WHERE IT COMES FROM

Welcome to The Deep science and technology column where we cover topics from the deep sea to deep space and beyond. Join us each week on Newstalk K57 on Wednesday night from 7 to 8 p.m. for exciting live science expeditions or listen live on our web site www.thedeepradioshow.com

One of the ‘cool facts’ about Guam is its closeness to the Marianas Trench and the Challenger Deep, the deepest spot in the ocean. We all know that it’s east of Guam, it’s really close, and that’s where all our earthquakes come from. But unfortunately, common knowledge can be wrong. For starters, the name of the trench is not the Marianas Trench; it’s the Mariana Trench (no ‘s’ on the end). And it doesn’t lie only to the east of Guam. The Trench is over 1,500 miles long and the deepest part actually lies to the south of Guam.

The deepest part of the Trench is called the Challenger Deep and its depth is variously reported as 35,760 ft, 35,798 ft, 35,810 ft, 35,813 ft, 35,838 ft, and 36,201 ft, depending upon the consulted source. I think this should give you some idea of just how difficult it is to measure depths in the ocean but whichever depth you choose, the deepest part of the Mariana Trench is almost SEVEN MILES deep. Toss Mt. Everest into that awesome chasm and it completely disappears. Guam is also not the closest point of land to the Challenger Deep; Fais Island in Yap is. And the lowest point on Earth isn’t particularly close; it’s 190 miles to the southwest of the island or father away than Saipan.

That part about the Trench being where all our earthquakes come from is true in a way. The floor of the Pacific Ocean is spreading at a rate of about ¾ inch each year. That spreading ocean floor is plunging beneath the small plate Guam rides on, to create this awesome chasm. All that melted ocean floor is lighter than the molten rocks beneath us and it bobs back up to form volcanoes in a process called ‘back arc spreading. .

All the island north of Saipan are active volcanoes and that arc extends past Guam with several volcanoes that are still below the ocean’s surface. That rising magma from the melted sea floor is making the volcanoes and causes our earthquakes. But why is the seafloor spreading?

An article in the 27 July issue of the journal Nature states that for the first time, scientists have found regions of the earth's crust which are stretching apart to form new sea floor along gently inclined tectonic faults called detachment faults.

The scientist studied an area of the mid-Atlantic ridge at 13 degrees North (Hmmm, familiar latitude!) and discovered that along 50 miles of this undersea mountain range; all of the new crust along one side was being formed through a chain of linked detachment faults each at a different stage of evolution. After a while, each fault becomes inactive, and is replaced by a newly-emerging fault.

Roughly one square mile of new ocean floor is created around the world every year. There are probably similar spreading centers off the coast of South America that create the sea floor that plunges beneath us in the western Pacific. Join us this week on The Deep as we go as deep as we can get!

The Deep is broadcast on Newstalk K57 every Wednesday night at 7:00 p.m. You can also listen live from our web site www.thedeepradioshow.com. Join Jim Sullivan, Pam Eastlick, and Peter Melyan on the deepest radio show on Earth.