February 13, 2012

Monday Geology Picture: Tarague Embayment, Guam

Posted by Evelyn Mervine

Tarague Embayment, Guam. Photograph courtesy of Jason Vanover.

My cousin Jason is in the Air Force, and he’s currently stationed on the island of Guam, which has some fantastic geology and also some gorgeous beaches. He’s been sharing some pictures of his travels around Guam, and I must admit I’m somewhat jealous of his travels. Perhaps I’ll have a chance to visit Guam one day. There certainly seems to be plenty of great geology to see there!

Guam is a volcanic island that is located at the southern end of a chain of volcanic islands associated with the Izu-Bonin-Mariana Arc, which formed as a result of the subduction of the Pacific Plate underneath the Philippine Sea Plate (and also the tiny Mariana Plate). Associated with the Izu-Bonin-Mariana Arc is the Mariana Trench, where the deepest part of Earth’s oceans is located. The volcanic islands of the Izu-Bonin-Mariana Arc formed as a result of volatiles being released from the subducting Pacific plate. These volatiles (mostly water and carbon dioxide) lowered the melting temperatures of the mantle underneath the arc, producing melts which created the volcanic islands.

Guam was built from volcanic eruptions starting around 43 million years ago. The most recent volcanic eruption on Guam was around 10 million years ago. Therefore, geologists do not anticipate that there is currently a high risk of a volcanic eruption on Guam. However, there are plenty of active volcanic islands located near Guam, as is shown in the USGS map below.

Map courtesy of USGS and taken from here: http://vulcan.wr.usgs.gov/Imgs/Gif/MarianaIslands/Maps/map_mariana_islands_volcanoes.gif

Because Guam hasn’t been volcanically active in about 10 million years, there has been time for carbonates (limestones) to form on top of some of the volcanics, and there are abundant coral reefs located offshore.  One place where some impressive carbonate deposits have formed on Guam is Tarague Embayment, which is shown in this week’s geology picture. The rocks are a little hard to see since they’re covered under thick green vegetation. Underneath that vegetation, though, there is a limestone cliff that was formed in the Pliocene-Pleistocene (within the last 5 million years or so).

My cousin Jason took some pictures during his visit to Tarague Embayment, and he was kind enough to let me share them here. Thanks, Jason!

Here’s a picture of a sign at the embayment with a little bit of geological information:

An information sign at Tarague Embayment. Photograph courtesy of Jason Vanover.

And here’s a picture of my cousin, looking handsome in his Air Force uniform:

My cousin hanging out at the embayment. Photograph courtesy of Jason Vanover.

Sorry, ladies! My cousin is happily married and has a beautiful little girl.