Haiti and the Dominican republic share a border on the Caribbean Plate. One crustal plate goes underneath the other (subduction zones),  this causes formations to occur underwater. Such activity is responsible for creating islands like the Caymans (https://www.csmonitor.com/World/Americas/2010/0121/Haiti-earthquake-Why-the-Caribbean-is-a-mini-ring-of-fire).
     There's a plethora of volcanic rock to see in Haiti, but no eruptions. There have been several earthquakes which may be the result of the subduction zones. Even though Haiti itself hasn't had an eruption, Mt. Pelee in Martinique is relatively close and erupted in 1932. It is considered the third deadliest volcano on Earth. It is constantly checked for deformations, variations of distance, and satellite recognition to make sure the people of Martinique are safe (https://mountpeleebyjuliaandmaddy.weebly.com/impacts-and-safety.html).
     Even though Haiti hasn't necessarily had an actual eruption, there are some very dangerous earthquakes that make up for it.