June 29, 2017

We Probably Should Have Waterproofed That: Terrestrial Volcanism

Posted by larryohanlon

By The Clemson Geopaths Team

Trailhead to Cold Soufriere

Yesterday we were investigating marine volcanism via underwater fumaroles, and today we’re exploring the terrestrial side of Dominica! Scott Brame, a professor at Clemson University, took us to some of the most interesting geological features this volcanic island has to offer.

To start the day, we traveled just down the road from where we are staying. Alongside the road, we stopped at a columnar basalt outcrop. These basalts exposed along the Imperial Highway here represent the earliest stage of island building, dated back only to the Miocene (7 million years ago) – Dominica is not very old! The columns form from horizontal flows of basalt and result as the basalt cools.

Section of columnar basalts in Antrim Valley

Then we made our way north along the coast and stopped near Coulibistrie to document evidence of island uplift. Dominica is growing as new volcanic material is added, and marine life preserved above sea level is great evidence of this. The outcrop contains staghorn coral that grew in the ocean and boulders that came from the land. These were mixed together in a shallow offshore setting and subsequently uplifted.

A lookout to the Caribbean through section of uplifted coral

After Coulibistrie we made another stop along the road and checked out a very colorful wall. This is the Du Blanc outcrop showing a block and ash flow deposit that has been hydrothermally altered.The red and yellow colorations denote different levels of oxidation and reduction of the minerals that were in the hydrothermal fluids.

An outcrop of hydrothermally altered block and ash flow

After going up and down more winding roads, we found a place to stop and get pictures and video of this beautiful feature. These surge deposits on the road just south of Toucari Bay represent gas and rock fragments ejected during a volcanic eruption with a much higher rate of gas to rock particles. The surge deposits display wavy bedding and are overall well sorted with rounded pumice lapilli. The deposit is underlain and overlain by block and ash flow deposits which indicate it might be associated with a volcanic dome collapse.

Roadcut view of surge deposits south of Toucari

We ended the day by hiking to one of Dominica’s coolest (in both senses of the word) spots: Cold Soufriere. The springs at Cold Soufriere offgas a significant amount of carbon dioxide and sulfur dioxide, the latter accounting for the pervasive smell of rotten eggs one encounters at the site. The origin of these springs has two possibilities: one, that the hydrologic system is no longer in contact with a magma source or two, that the magma has cooled sufficiently but still contains abundant dissolved gases.

Professor Brame, Emily, Sawyer exploring the sulfur springs

We hope you enjoyed following along with our team as we explored some of the many geological wonders of Dominica! To keep up with our future adventures or check out our previous ones, follow us on twitter, instagram or facebook @clemsongeopaths!

The Clemson GeoPaths Team is headed by Dr. Stephen Moysey and Dr. Kelly Lazar who work under a NSF grant for geoscience education, with a goal of promoting geoscience through interactive experiences. This summer, the students involved include Stephanie, Emily, Sawyer and Katrina.