End of Mission Report: United Nations Disaster Assessment & Coordination (UNDAC) Brava Emergency, Cabo Verde November/December 2023

1. Background Information on the emergency

1.1. Description of potential disaster

Brava, the tiniest island by area (64km²) and population (5,647 inhabitants, INE, 2021) of the Cabo Verde archipelago, was placed on contingency and alert status by the Government of Cabo Verde on 22 November 2023 for a (renewable) period of four months, following recurrence of events depicting increased seismic instability.
Chronology of events • 30 October: A low-magnitude seismic event (4 to 4.5) is recorded a few kilometres off the coast of Vinagre and Aguada in the east of the Island.

• 9 November onwards: The occurrence of a continuous signal starts to be observed, with variable intensity and specific spectral peaks (e.g. 3, 6 12 cycles per second). This signal, called harmonic tremor, is interpreted as being produced by the flow of gases of volcanic origin.

• 15 November onwards: The situation worsens with more intense episodes of volcanic tremor, long-period events (caused by the shock of magma movement) and burst events (identical events recorded with a few seconds of separation) recorded. Felt earthquakes become more frequent and the seismic rate increases. Epicenter of the seismic activity is in the north of Cova Joana, in the center of the island.

• 20 November: Taking this set of changes into account, the National Institute of Meteorology and Geophysics (INMG), in charge of real-time monitoring of seismic activities, informs the press of the possibility for further deterioration in coming days, although eruption probability remained assessed as low.

• 22 November: The Government through the Minister of Internal Administration (MAI) declares a state of contingency and alert for four months for Brava Island, per to the occurrence of frequently felt earthquakes, which means an increased accumulation of magma at the base of the island. Support is requested from the UN System.

• 30 November: Following reduce seismic activity, the National Civil Protection and Firefighters Service (SNPCB) downgrades the alert level to two.

• 8 December: SNPCB reduces alert level to one, following return to routine seismic activity.

Hazard characteristics

There are no reports of eruptions in Brava since human presence in the Cabo Verde islands in 1460. It is believed the last eruption could have happened in the Holocene (> 10,000 years). Brava nevertheless shows geological evidence of different type of volcanic activity that Fogo Island, its closest neighbor located 20 km away, which recorded its last eruption in November 2014 to February 2015, resulting in the evacuation and displacement of 964 people and significant damage (evaluated at $28 million by a Post-Disaster Needs Assessment). According to geological studies, Brava shows clear evidence of a destructive and explosive type of volcanism. The Plinian volcanism is mostly characterized by photolytic lavas and ashes. These tend to be spectacularly explosive eruptions associated with volatile-rich dacitic to rhyolitic lava, which typically erupts from stratovolcanoes. These eruptions are highly variable, from hours to days.

Population, access and infrastructure

The distance from north to south of the island is approximately 10 km, approximately 8 km from east to west; the highest point is 976 m. The island’s main populated area is Nova Sintra, with other localities scattered throughout the island (Furna, Faja de Agua, Nossa Srª do Monte, Campo Baixo, Lomba Tantum, Escovinha, Cova Rodela, Mato Grande, Cova de Joana, Benfica, Cachaço).
The road network is limited, with no alternate axis shall the main road be blocked by magmatic extrusion. The island has one small port in northeastern side in Furna. Two other points of access to the sea (Faja d’Agua and Tantum) could also be considered in case of evacuation, as per the 2016 contingency plan.
According to the last detailed census of the population undertaken in 2021, the total population of Brava Island is 5,647. Brava’s population is made of 52% of men and 48% of women, with 3.1 as family size. 1,121 are under the age of 15 and 595 over 60 years. 745 live with a disability, including 569 in rural area. Brava’s population is mostly rural (60.1%), against the national average (25.9%). 39 nationals of other countries are residing in the island.
Brava is home to 2,357 buildings, 92.4% of which are dedicated to housing. 96% of houses in Brava are linked electricity and 88% to water systems. 85.4% of houses possess latrines or toilet.

1.2. Impact of potential disaster

There is great uncertainty about the localization of a potential eruption, which can only be identified by earthquakes.
According to SNPCB, a simultaneous eruption in different locations of the island would be a likely scenario. As the volcano has not erupted since the island was populated, predictions of its behavior during an eruption are difficult to make, but it will likely be more explosive in the north of the island and effusive activity in the south.
Landslides will possibly make evacuation via roads unfeasible. The hot ash, gases, falling rock fragments and lava can cause burns severe enough to immediately kill the population.
Secondary dangers are also a possibility for neighboring islands, given the potential for generating tsunamis and ash clouds.
It is anticipated that a preventive mass evacuation of the island will be necessary, due to the small size of the island (thus leaving no safe area to which people could be transferred). The SNPCB informed that in case of reaching level 4 status, chances of an eruption are assessed at 75% by INMG, leading to immediate evacuation of the island. In later discussions with SNPCB and the Minister of Internal Administration, consensus was reached on the need to define and institutionalize a ‘3.5 level’ triggering a pre-evacuation, in order to have sufficient time to complete it ahead of an eruption, in view of logistical constraints.
The planning hypothesis is that displaced people should be transported to Fogo, where long-term community support is required, until a decision could be made on resettlement or more permanent relocation.