We first set out for the Grand Savanne ignimbrite. An ignimbrite is a deposit of a pyroclastic flow, resulting from a collapsed eruption column of an explosive volcanic eruption (see image below). We characterized the stratigraphy exposed along a beach on Dominica's west coast. The bottom layer, characterized by angular fragments, is a block and ash flow, overlain by a fossil soil known as a paleosol. This paleosol exhibited a distinct orange color which is a "baked contact". This baked contact was a result of the transition of ferrous iron to ferric iron, a form of oxidation. The paleosol is overlain by a welded tuff, a compacted ash deposit. Overlying the welded tuff is a pyroclastic flow and ashfall deposit, indicative of numerous eruptions in the area.
We then traveled to "surprise beach" with an employee from the Office of Disaster Management of Dominica (see below). The principal of the local school shared her first hand account with us of how Surprise Beach had formed. The original coast at this location was a cobble to boulder sized rock beach with no sand. A river less than three kilometers away had experienced a landslide that effectively dammed the river. As the water accumulated behind the loose sediment of the dam, the pressure of the water eventually broke through the dam and washed the sediment into the ocean. Over the course of months sand began to accumulate along the coast, creating a brand new beach for the island of Dominica.
- Justin & Sarah