Our thoughts are with Haiti. Tragically, on 14 August 2021 at 8:29am (local time), a shallow (10km) earthquake of 7.2M occurred on the South West peninsula of Haiti 13 kilometres southeast of Petit Troup de Nippes. The earthquake was felt across the region, including Haiti, Dominican Republic, Jamaica, Cuba, and Puerto Rico. Over one million people may have been exposed to very strong or severe shaking.
A one-month state of emergency has been declared for Haiti. As of 16 August 2021, 1,419 are believed to have lost their lives, more than 6,000 injured and many thousands displaced. Tropical Depression Grace is likely to pass over the stricken area at the time of writing, bringing with it the risk of heavy rains, flooding, landslides and further loss of life.
Aftershocks are occurring, and may do so for some time. There is a small risk that this event is a foreshock to another event.
Haiti is located on the western side island of Hispaniola in the Greater Antilles Archipelago; the Dominican Republic occupies the eastern side of the island. Two large fault zones cross the island: the Septentrional-Orient fault in the north and the Enriquillo-Plantain Garden Fault Zone in the south.
Hispaniola was formed from the collision of volcanic arcs with the North American Plate; the island is made up of 11 former island arcs. Haiti has an estimated population of 11.4 million (2018). The country is poor, politically unstable and yet to recover from the 2010 earthquake.
While the island has a volcanic past, there has not been any reported volcanic activity in the Holocene. There are two Pleistocene volcanoes in Haiti, the nepheline basalt scoria cones of Morne la Vigie, north of Port au Prince, and Thomazeau, east north east of Port-au-Prince, both of which were active around 1.5 million years ago; and, three in the Dominican Republic, the basaltic cinder cones of San Juan, trachyandesite lava domes and flows of the Dos Hermanos volcanic field and the rhyolitic to basalt Valle Nuevo volcanic field. The presence of picrite in the Duarte Complex in central Hispaniola and enriched basalts in southern Haiti are thought to be indicative of earlier hotspot activity
Tektites have been found in the Beloc Formation, Haiti, which are thought to have originated from the asteroid impact in Yucatán Peninsula, Mexico, which caused the K-Pg mass extinction event 66 million years ago.
2021 7.2 M Earthquake
The earthquake occurred in the Enriquillo-Plantain Garden Fault zone on the transform plate boundary between the Caribbean Plate and the North American Plate. The faulting mechanism for this earthquake indicates oblique thrust faulting along the fault zone. This fault zone accommodates 7mm per year of the 20mm per year of the relative plate motion. It is likely that this earthquake occurred in the same fault system as the devastating January 2010 7.0M earthquake which occurred near Port-au-Prince, the capital.
2010 7.0M Earthquake
According to the DEC, the January 2010 earthquake not only caused significant loss of life and damage but also severally impacted Haiti’s government and infrastructure: 25% civil servants died, 60% government buildings, 80% schools in Port-au-Prince and 60% schools in the South and West departments were destroyed. In all, over 220,000 were killed, more than 300,000 injured and around 300,000 homes damaged or destroyed.
USGS note that four other large earthquakes are known to have occurred in the region: October 1751 in the Gulf of Azua at the eastern end of the Enriquillo-Plantain Garden fault zone; November 1751 at Plaine du Cul-de-Sac which destroyed Port-au-Prince; June 1770 which also destroyed Port-au-Prince; and, April 1860 which also caused a tsunami.
On 4 December 2020 the alert level for Mt. Pelée was raised to yellow due to increasing seismicity above background levels; and, on 29 December 2020 the alert level for La Soufrière St. Vincent was raised to orange following an increase in seismic activity, changes seen in the lake and fumaroles and a new growing lava dome emerging in the summit crater.
This led us to look into what drives volcanism in the area, notably the interaction of the Caribbean Plate with its surrounding plates.
Mt. Pelée is famous for destroying the town of Saint- Pierre and its inhabitants plus visitors – a total of 29,000 people – in a matter of minutes on the morning of 8 May 1902 in a pyroclastic flow during a VEI 4 eruption. La Soufrière St. Vincent also erupted around the same time. Both volcanoes are located in the Lesser Antilles on the Caribbean Plate.
Mt. Pelée is located on Martinique. She is a 1,400m high stratovolcano located in the caldera of an earlier volcano; edifice failures have breached the south west section of the caldera. Her lava types are andesite, basaltic andesite, dacite and basalt, picro basalt.
54 Holocene eruptions are recorded by GVP. Her historic eruptions include 1792 (VEI 1), 1851 (VEI 2), 1902 (VEI 4) and 1929 (VEI 3). Two lava domes were emplaced in the summit crater, l’Etang Sec, during the 1902 and 1929 eruptions.
Prior to the 1902 eruption, Mt Pelée’s known eruptions had been mild. Activity at the volcano started to ramp up gradually with fumaroles in the summit crater in 1889 to March 1902. From 23 April 1902 phreatic activity cleared out old rock, starting with minor explosive activity. By 4 May 1902 ash was raining down on Saint- Pierre. On 5 May, 23 people were killed when near boiling water from the crater heated by rising magma overran a distillery in a lahar in the Rivière Blanche valley.
On 6 May 1902, new lava emerged creating a lava dome. During 7 May 1902, small parts of the dome collapsed. At 07:50 on 8 May 1902, explosions were heard and a large black cloud seen to emerge and flow down the volcano, engulfing Saint-Pierre and some of the ships in the harbour. Most of the casualties were killed by hot gases and dust from the blast. Several pyroclastic flows followed: on 20 May 1902 a second pyroclastic current swept over Saint-Pierre destroying several of the remaining buildings; the Rivière Blanche valley saw several PDCs over the ensuing months; and, Morne Rouge was destroyed and 2,000 people killed by a pyroclastic current on 30 August 1902. During this activity a 300m lava spine emerged. After this eruptive activity continued until 1903. The lava spine has since been eroded.
Saint-Pierre had not been evacuated prior to 8 May 1902 for a couple of reasons: it was not known at the time that the volcano produced pyroclastic flows so the danger was not understood; and, an election was due on 11 May 1902, which politicians were keen should go ahead. No evacuation order was given.
When activity ramped up again prior to the 1929 eruption, people were evacuated in time.
La Soufrière St. Vincent
La Soufière St. Vincent can be found on St Vincent Island. She is a 1,234m high stratovolcano with crater lake and lava domes. The 1.6km wide summit crater is located on the south west edge of a 2.2km wide Somma crater; slope failure caused a breach in the Somma crater. Her lava types are andesite, basaltic andesite and basalt, picro basalt.
22 Holocene eruptions are recorded by GVP. Her historic eruptions include 1718 (VEI 3), 1812 (VEI 4), 1902 (VEI 4), 1971 (VEI 0) and 1979 (VEI 3). The 1902 eruption occurred on 6 May 1902, killing 1,680 people. The 1812 eruption produced a new crater, cutting through the summit crater. 1971 eruption extruded a lava dome in the summit crater, which erupted explosively in 1979 to be replaced by another dome.
As noted above, both Mt. Pelée and La Soufrière St. Vincent are located on the Caribbean Plate in the Lesser Antilles. The Caribbean Plate is thick oceanic crust located between the North American and South American Plates. The northern boundary of the Caribbean Plate is a transform boundary with the North American plate, running from Central America to the Virgin Islands. The Gonâve microplate and Puerto Rico Trench form part of the northern boundary. At the eastern boundary, the South American Plate subducts under the Caribbean Plate in the Lesser Antilles. At the western boundary, the Cocos Plate subducts under the Caribbean Plate, forming the Central American Volcanic Arc. The southern boundary with the South American plate is a complex, comprising a convergent margin with the Panama Plate, a subduction zone with the North Andes Plate and a transform boundary with the South American Plate. The main plates velocities relative to the African Plate are noted below.
North American Plate
25 mm per year
67 mm per year
10 mm per year
19 mm per year
Coiba and Malpelo Plates
North Andes Plate
23 mm per year
40 -53 mm per year
South American Plate
27 – 34 mm per year
The origins of the Caribbean Plate are debated. There are two main theories which attempt to explain why the less dense but thicker crust of the plate overrides the Cocos and South American Plates. It may have evolved millions of years ago from the Caribbean large igneous province, formed at the Galapagos hotspot, drifting to its current location as the plates moved to accommodate the widening of the Atlantic Ocean. Alternatively, it may have formed from an old hotspot in the Atlantic. These theories are based on the relative motions of the plates. The first theory works on the basis that the Caribbean Plate is moving eastward compared to the North and South American Plates, whereas the latter uses the actual westward motion of the Caribbean Plate.
Yes, we’ve downloaded earthquakes for the region from USGS’s earthquake search, taking a larger area than the Caribbean Plate in order to pick up the subduction zones. In this case, it was not really necessary as most subduction is beneath the Caribbean Plate, but it was fun to find several microplates in the process: the Gonâve, Panama, Coiba and Malpelo Plates. The Malpelo Plate was first identified as late as 2017 by Tuo Zhang, Richard G Gordon et al of Rice University.
The coordinates selected were: 3.760°S, 107.051°W to 26.838°N, 48.867°W for earthquakes with magnitudes of 2.5 or more between 1 January 1975 and 5 January 2021. This picked up 80,751 earthquakes.
From Figs 2, 3 and 4 below, we can see the plate boundaries and the subduction zones on the western and eastern margins of the Caribbean plate are well marked by earthquakes and volcanoes; the subduction of the Caribbean Plate under the North Andes Plate is also visible (lower centre of the depth plot); and, the Puerto Rico Trench is also tectonically very active. The Puerto Rico Trench has produced some large earthquakes and tsunamis.
Fig 4 shows subduction of the North American Plate on the right of the depth plot. But there is also a line of earthquakes on the left of the plot which appears to indicate another subduction zone. Neither subduction zone here, despite being seismically active, has active volcanoes associated with it. It’s possible that there is another microplate here, but this is conjecture on our part until we can find an explanation or confirmation.
If you are interested or concerned by the alert statuses of Mt Pelée and La Soufrière St Vincent, you can find more information at L’Observatoire Volcanologique et Seismologique de Martinique, the National Emergency Management Organisation (NEMO) or GVP.
Hope you enjoyed our little tour. We will be looking in more detail at points of interest in the future.
Zhang, Tuo; Richard G. Gordon; Jay K. Mishra, and Chengzu Wang. 2017. The Malpelo Plate Hypothesis and implications for nonclosure of the Cocos-Nazca-Pacific plate motion circuit, 1. AGU Fall Meeting, New Orleans. Accessed 2018-06-06.
“Volcanoes”, Peter Francis and Clive Oppenheimer, Oxford University Press, Second Edition, 2004.