1520 eruption of Volcán de Fajardo

### Impact

* At least 5,000 deaths from direct volcanic effects; 20,000 deaths from post-eruption famine on the island.
* Thousands left homeless due to the effects of ashfall.

The **1520 eruption of Volcán de Fajardo** in northern Puerto Rico was the most powerful volcanic eruption to have been occurred historically on the island and the deadliest natural disaster to date on the island. The volcano ejected an estimated 3.7 cubic kilometers (0.9 cu mi) of material, most of which was erupted during the devastating lateral blast on April 19, 1520. This left a bowl shaped caldera in place of the stratocone that existed several days prior.

The eruption began on March 28, 1520 after local officials noted black and white near Fajardo's summit. 2 days later, a much larger explosion carved out a crater at the summit where the majority of the subsequent explosions occurred. On April 2, a group of soliders sent by the island's governor, Antonio de la Gama reported that local natives have felt increasingly larger "*temblor*" (ground shaking) and that the color of the smoke being generated by the volcano had become a dark brown coloration. This is likely the first historically reported magmatic eruption of the volcano sine colony rule began. On April 17, a large explosion was heard from the islands capital of Puerto Rico (modern day San Juan). Geologist's and Historians believe this was the first sign of the eruption starting to reach its climax. The following day, an group of soliders reported to their commander the frequency of explosions was increasing and the smoke column continued to persist. This phase of activity lasted until midnight when the explosions ceased to be heard. Early on April 19, many in Puerto Rico awoke to massive loud explosions, likened to explosions of hundreds of cannons by one official. The governor noted in his journey that a "large black cloud extended from the mountain to the sea and a large column of smoke extended into the heavens". The people did not know it, but the northern flank of Fajardo had just catastrophically collapsed and was followed by a lateral blast, similar to the 1980 eruption of Mount St. Helens. It is unknown when the climatic phase of the eruption ended but varying reports cite either late evening April 19 or early on April 20, during which explosions became less frequent and then ceased. The large pyroclastic surge and ash cloud also dissipated, marking the end of the main phase of the eruption.

The colonial government attempted to mount multiple expeditions toward the missing mountain but were forced to turn back due to extremely hot deposits of ash and continued smaller eruptions in the crater. On July 17, a spanish corporal described the aftermath of the eruption in detail based on his observations from an expedition that reached the newly formed caldera rim 2 days prior. His account described 5 small lakes within the crater and a vast field of "grey dust as deep as a man's knee" toward the north, likely describing the still cooling ash deposited by the surge on April 19. Various other officials noted grey sand falling in villages and towns near the volcano and causing the water to turn foul. They also noted crops failed in any area wherever the dust fell and that it became similar to mud when it was exposed to rain.

The eruption continued, being limited to the caldera rim until August 15 when the last known explosion occurred in one of the lake. Following this the volcano entered a phase of dormancy that lasted until 1817.