The island on which Haiti is located is a mountainous and tectonically active island with folded rocks*, earthquakes, raised coral reefs* and submarine basalt*. Complex folding, faulting, mountain building and brittle rock deformations in much of Haiti is the result of transpressional* forces between the North American and Caribbean tectonic plates, extending and dissecting the island.
*Folded Rocks - Folded rocks are igneous rocks that are forced to bend into U-shaped or upside down U-shaped formations down near the earth's core before being pushed above sea level from the pressure of shifting or colliding tectonic plates.
*Raised Coral Reefs - Coral reefs are underwater structures composed of the skeletons of colonial marine invertebrate. They form on underwater volcanic peaks, then rise above sea level under high pressured tectonic plate forces. They contribute to a very diverse soil and indigenous species of flora and fauna.
*Submarine Basalt - Submarine basalt forms when the lava from underwater volcanoes cools quickly. The rock crystallizes on the ocean floor and then rises above sea level.
*Transpressional Forces - A term used when tectonic plate forces create a strike-slip shear, or when there is an oblique striking between them.
"The deadly earthquake of January 2010 and recent earthquake of 14 August 2021, are reminders of the active tectonic forces that are still shaping the island of Hispaniola. The geology of Hispaniola consists of a core of intrusive igneous rocks which forms the backbone of the island, near the northern border between Haiti and the Dominican Republic. This core is surrounded by uplifted and deformed sedimentary limestones and shales, volcanic and volcaniclastic rocks, and valley-filling alluvium in a series of roughly east–west-trending mountain ranges.
"The details of the geology of Haiti have been well described by previous researchers. This report focuses mainly on the limestone formations, karst features, and the karst aquifers and springs that serve as a primary water source for many rural Haitians.
"Bedrock lithologies in Haiti are dominated by calcareous rock units and alluvium which make up roughly 84% of the surface area of Haiti. These lithologies often contain shallow unconfined aquifers that are susceptible to contamination by inadequate sanitation services and by improperly placed or constructed pit latrines.
"Many of the durable limestones have fissures and fractures which have been enlarged by dissolution in a process typically referred to as karstification or simply “karst”. Lack of protective soil cover in many parts of Haiti due to deforestation and erosion has made many unconfined karst aquifers particularly vulnerable to contamination with water-borne pathogens. Karst development and dissolution is enhanced locally by faulting, folding, and deformation associated with tectonic forces."
Note: A karst landscape is one where in the dissolving of bedrock, sinkholes, sinking streams, caves, springs, and other characteristic features are created. It is primarily associated with soluble rock types such as limestone, marble, and gypsum. It means that very little water flows on the surface, and most rapidly enters the ground. Thus, water accumulates in subterranean reservoirs, known as tropical caves.
"The development of karst dissolution cavities and caves varies considerably in different limestone units with some exhibiting extensive caves and karst conduits, while others have almost no karst or evidence of karst dissolution. No systematic mapping of the cave formations has been identified; however, available mapping suggests there are at least 150 caves located in several regions with greater cave and karst density.
"In many karst regions, well-developed weathering of limestone and thick soils, collectively referred to as epikarst, serve as an important primary filter for pathogens. Haiti is exceptional in that many limestone outcrops have thin to nonexistent soil cover. The removal of this natural filtration system is primarily the result of erosion, deforestation, and agricultural practices.
"Near major rivers, and in the large basin occupied by Port au Prince, sufficient alluvium has accumulated to form alluvial fans and extensive alluvial aquifers and floodplains. These aquifers, although more effective at filtering pathogens than karst limestone, are also prone to contamination from the installation of shallow hand-dug wells in many rural and semiurban settings."
Source | Springer Link Hydrogeology Journal Article (March 26, 2022). Illustrations, links, and reference citations included.
| CLICK to see how water moves through a karst landscape (2:43min)