When and how was Guam formed?

  • Published
  • By Joyce I. Martratt
  • 36th Wing executive assistant to the commander
As I was reading some background on Guam's origin and about the Marianas Trench, I came upon an awesome graphic of what lies beneath and the neighboring trench.

Imagine the areas surrounding Guam without water--all you will see are mountains of volcanoes and a nearby crevice known as the Marianas Trench, the deepest place on earth.

Geologists have stated that the island of Guam and the Marianas Islands were created millions of years ago by active volcanoes. Guam is the largest of the group which includes Rota, Saipan, Tinian, Agrihan, Anatahan, Alamagan, Pagan and Aguijan (Aguijan is the only uninhabited island among the group).

Visualize these mountains of volcanoes shifting and forming millions of years ago, sinking beneath the ocean but on top the Marianas Trench's floor. The southern lava volcano merged with the older northern one, leaving only their twin peaks above sea level forming the island we now know as Guam. The island is 212 square miles--30 miles in length and 8.5 miles width in the northern tip and 11.5 miles in the south.

Through research I discovered that Guam has two basic geological compositions. The central and northern parts of the island are composed of limestone with Mount Santa Rosa and Mount Mataguac having several volcanic formations. The southern part is volcanic with elongated mountain ridges, which divide the inland valleys and coastlines.

The island rests a few miles west of the Marianas, the world's deepest trench. The trench's depth extends to 6.79 miles below sea level and exerts a pressure level over 18,000 pounds per square inch.

I read that it would take a metal object 64 minutes to fall from the surface of the ocean to the bottom of the Marianas Trench, east of Guam.

The Marianas Trench is called the "Grand Canyon of the Pacific." It is recorded that many tremors and earthquakes occur; the vast majority are registered with a seismograph and not usually felt by the residents.

Guam straddles the edge of two overlapping tectonic plates: the Philippine Plate and the Pacific Plate. National Geographic called this area a subduction zone. This means the melting of rock produces magma that contains a lot of water. When the magma reaches the surface, the water expands very rapidly and launches the magma which is why the island-arc volcanoes are so explosive. National Geographic further iterated that "the water and sulfur mix gives these volcanoes a bang."

The deepest part of the Marianas Trench is the Challenger Deep--named after the exploratory vessel HMS Challenger II, a fishing boat converted into a sea lab by Swiss scientist Jacques Piccard.

Submarines use part of this long system trenches which circle the Pacific Ocean and which connect Japan and Kuril trenches. It reminds me of underground subway stations.

There are at least 22 trenches identified; 18 in the Pacific Ocean; 3 in the Atlantic Ocean, and one in the Indian Ocean. The Marianas Trench is the deepest at 36,201 feet or 6033.5 fathoms deep--over 8 tons per square inch pressure in the deepest part; coordinates are 11"21' North latitude and 142" 12' East longitude; 2, 1,580 miles long and 43 miles wide.