Smithsonian Institution
Global Volcanism Network Bulletin v. 20, no. 3, March 1995

Fogo (Cape Verde Islands)  New eruption on 2 April generates lava
      flows within the caldera

SW Cape Verde Islands, Atlantic Ocean
14.95N, 24.35W; summit elev. 2,829 m
All times are local (= GMT - 3 hours)

A fissure eruption that began the night of 2-3 April produced lava
flows from the base of the Pico cone, located within the
8-km-diameter Cha Caldera (figure 1). This cone, also called Fogo
Peak, has a crater ~500 m in diameter and 180 m deep. Caldera
residents felt weak intermittent earthquakes as early as 25 March.
After 0100 on 2 April the earthquakes increased in frequency, and
felt events occurred at 0700 and 1500. At about 2015 residents felt
a stronger earthquake that caused dishes to fall from cupboard
shelves and may have opened a 200-m-long crack on the flanks of the

Residents in Sao Filipe, ~15 km WSW of the vent, noticed a red glow
around 2300 on the night of 2 April, probably the beginning of the
eruption. Other residents reported that eruptive vents on the flank
of Pico opened at 0006 on 3 April. Initially there was a burst or
jetting of gas followed by ejection of large blocks. This
Strombolian activity was followed by a "curtain of fire" that fed
a lava flow, which cut off the main road to Portela village by 0200
(figure 2). By 0500 on 3 April, fine dark ash had begun to fall in
areas close to the volcano. Around the same time, an eruption cloud
to a height of 2,500 m was formed. Witnesses told reporters that
the volcano was "spewing out smoke and flames." The head of the
Cape Verde Red Cross stated that high flames could be seen and that
"a pall of black smoke was hanging over the island."

During the night of 2-3 April, several residents evacuated to the
N coast. Once ashfall began, more caldera residents and some people
in the eastern villages of Corvo, Achada Grande, Relva, Tintiera,
Cova Matinho, Cova Figueira, and Est ncia Roque also evacuated to
the coastal towns of Mosteiros (~9 km N of the summit) or Sao
Filipe. Police officials reported that all of the ~1,300 people
living within the caldera had managed to get out on foot and had
been accounted for by noon on 3 April.

Under the supervision of the National Defense Minister, a Crisis
Cabinet was created by the Cape Verde Government. About 60 Cape
Verde Army soldiers were sent to the island and an emergency
communications system was installed. Food and medicine were
provided, and evacuation centers (schools, private institutions,
and tent camps) were established to hold up to 5,600 people.
Official reports indicated that almost 1,000 persons were sheltered
in the Army camps at Sao Filipe, Patim, Achada Furna, and
Mosteiros. During the first days of the eruption local authorities,
Cape Verde soldiers, and volunteers, helped caldera residents save
their belongings. Nobody was killed, and only 20 people needed
medical assistance during the evacuation, including children with
respiratory problems. Although numbers are uncertain, as many as
5,000 people may have been displaced during this eruption. As of 16
April, Portela residents continued to remove belongings by foot.

Around noon on 3 April some teachers who had driven from Sao Filipe
to Mosteiros told geologist Veronica Carvalho Martins (U.S. Embassy
in Cape Verde) of sandy ashfall along the road on the E side of the
island just below the caldera; they also reported sounds "like an
old stove." During a flight W of the caldera soon afterwards,
Martins observed a high mushroom-shaped ash column rising from the
caldera. Martins later saw a long fissure vent with lava fountains
feeding an already well-developed flow that was moving W across a
road towards the caldera wall and curving N. A vent SE of the
fissure exhibited continuous strong ejection of brownish
pyroclastic material, while to the NW a smaller vent was
intermittently ejecting similar material.

Jo~o Gaspar (Universidade dos A ores) and colleagues from Cape
Verde (ISE and IICT) reported that on 3 April a thick cloud of dark
ash and vapor 2,500-5,000 m high could be seen from Santiago
Island, ~60 km ENE. Early that morning three small vents were
observed inside the caldera along the SW part of a N30E fissure
that crossed the main road within the caldera (figure 2). Fine dark
ash and small pahoehoe lavas were produced, and large plastic bombs
(1-4 m in diameter) were projected distances of 500 m. That
afternoon the fissure reached 2 km in length, and four new vents
opened in its NE section. Activity increased during the night of
3-4 April with the emission of more lava flows, but decreased the
following morning. One Cape Verde official said that the lava was
moving at a speed of 60 m/hour. Gaspar reported that explosive
activity was centered at the NE vents, but strong fumarolic
activity continued along the main fissure. Lava fountains reached
~400 m high and a cloud of dark ash and gases rose 2,000 m. A
scoria cone with a crater open to the SW formed and produced aa
lava flows with thicknesses of 3-10 m measured at different fronts.

Effusive activity remained intense on 4 April, but ejection of
pyroclastic fragments had decreased significantly. Television
pictures showed a lava "stream" coming from the fissure and, in the
morning, a mantle of aa lava covering the central part of the
caldera. Portuguese television and other press coverage on the
evening of 5 April indicated that activity had decreased.

In the following days the lava flow reached the settlement of Boca
de Fonte near the caldera wall ~2 km W of the eruption center, and
by 9 April it had destroyed at least 5 houses (possibly 10), the
main water reservoir, and several square kilometers of fertile land
used to grow coffee, wine grapes, fruits, maize, tapioca, and
beans. Reluctant farmers with cattle in the caldera were ordered to
leave their homes or face arrest on 8 April. A TSF Radio
correspondent reported on 9 April that the lava flow moving into
Boca de Fonte was advancing at a rate of 10-14 m/hour, twice as
fast as the day before. However, the flow slowed to 4-5 m/hour on
the 10th. Weak tremor had been felt on the caldera floor since the
start of the eruption. On 10 April the seismicity increased, and
earthquakes with Mercalli intensities of III-IV occurred, probably
due to obstruction of the main vent, where lava fountaining stopped

Richard Moore and Frank Trusdell (U.S. Geological Survey) arrived
on 10 April to assess the volcanic hazards and advise the
Government of Cape Verde. With the help of Martins, they installed
a seismograph ~1 km S of the erupting vent. The seismograph
recorded continuous tremor, indicative of the ongoing eruption, as
well as microearthquakes (M <1) at 0759 and 1213 on 12 April.
Volcanic tremor amplitude remained moderate to strong through 13-16
April. Lava temperature measured using a thermocouple on 11 April
was 1,026 deg C; this temperature seems low, but the aa was highly
viscous and sluggish, in contrast to the more fluid lava of Kilauea
in Hawaii. Lava flows and spatter contain ~5% black pyroxene and 1%
olivine phenocrysts, often together in clots.

Gaspar noted that on 11 April two main lava rivers had velocities
of 5-6 m/s near the vent. One lobe moved towards the W and fed the
flow-front moving towards Portela and Bangaeira villages. The other
more active lobe was directed SW into the Cova Tina depression. The
USGS team observed relatively low-volume eruptions of gas-rich
spatter slowly building a cone, and lava cascading rapidly down the
W flank of Pico being directed W and SW by high levees. The N
flow-front, near Portela, stagnated during 10-11 April. At 1830 on
11 April, advancing flows were confined to the S part of the
caldera, where two small lobes were moving W at a rate of ~15-20
m/hour, travelling S of the flows erupted the previous week.

During the morning of 12 April eruptive activity consisted of
Strombolian gas-rich spatter ejection; volumetric output remained
relatively low. At 1549 activity changed to Hawaiian-type fire
fountains that typically rose 100-120 m above the vent, slowly
building a scoria cone 100 m high. A new lava flow that started on
12 April overrode the first flow, which had stagnated ~1 km SW of
Portela. This flow quickly traveled 3 km from the vent in the
general direction of Portela, but remained entirely on top of the
first flow. All other lava flows were inactive at 1900 on 12 April.
Preliminary estimates of erupted volume through 12 April ranged
from 50 to 75 x 10^6 m^3 of lava.

Although volumetric output remained low, Hawaiian-type fire
fountains continued on 13 April and a flow confined to a 3-m-wide
channel cascaded down the W flank of the new cone. That channel
continued to feed a sluggish aa flow moving W then N. The cinder
and spatter cone reached a height of 120 m. The overriding lava
flow only moved N another 46 m; most of the additional lava was
expended covering the first flow. The added mass on top of the
first flow also caused it to spread laterally.

Activity on 14 April continued unabated, increasing the height of
the new cone to 130 m. The E lobe of the second flow reactivated
and moved 470 m N during 13-14 April. At 1900 on 14 April the
second flow was within 235 m of the distal end of the first flow,
and lateral spreading was occurring at the flow margins. At this
time the distal portion of the first lobe showed signs of renewed
movement, induced by pressure from the overriding aa flow. The
thick aa flow continued to spread slowly W the next day; maximum
lateral spreading S of Boca de Fonte was ~3 m. The new E lobe of
the second flow advanced an additional 6 m and stopped. At 1700 on
15 April the most active part of the overriding flow was on its NW
side. Much of the lava production apparently went towards
thickening the central part of the flow, estimated to be 16 m
thick. At 1800 on 15 April spatter fountains were ~100 m high and
cinder was falling as far as 2 km S of the vent.

Activity remained generally constant on 16 April, with fire
fountains typically rising 100-120 m; the scoria cone stood 140 m
tall. Estimates of lava-channel dimensions and speeds through 16
April yielded an erupted lava volume of 2.5-8 x 10^6 m^3/day. The
flow-front became remobilized at 1535 on 16 April, and by 1700 had
moved 38 m beyond and NE of the distal end of the first flow. At
that time the lava front was ~534 m from the nearest house in
Portela. A lava temperature of 1,056 deg C was measured with a
thermocouple in a spiny aa breakout near the terminus of the flow.
>From a few hundred meters away, USGS geologists watched the roof of
a small house burn; it was buried soon thereafter. There was also
considerable lateral spreading of the flow S of Boca de Fonte on 16
April. In this area, the flow-front monitor lines showed westward
movement of 19-26.5 m. At 1800 the flow was still active and 41-72
m E of the Portela access road. Thickness at the margins of the
active flows ranged from 1 to 20 m. The greater thicknesses are a
strong indication that a breakout of spiny pahoehoe or aa can be
expected, advancing the flow.

Fogo Island (476 km^2), with a population of ~33,000, consists of
a single massive volcano with an 8-km-wide caldera breached to the
E; the W rim rises 700 m above the caldera floor. The central cone
in the caldera, the highest point in the Cape Verde Islands, was
apparently almost continuously active from the time of Portuguese
settlement in 1500 A.D. until around 1760. Later historical lava
flows reached the E coast. The last eruption was during June-August
1951 from caldera vents S and NW of the central cone. That
eruption, also preceded by earthquakes, began with ejection of
pyroclastic material that formed Mt. Rendall and Mt. Orlando
(figure 2).

Reference: Neumann van Padang, M., Richards, A.F., Machado, F.,
Bravo, T., Baker, P.E., and LeMaitre, R.W., 1967, Catalogue of
active volcanoes of the world including solfatara fields, part XXI,
Atlantic Ocean: Rome, IAVCEI, 128 p.

Information Contacts: Jo~o Gaspar and Nicolau Wallenstein,
Departamento Geoci ncias, Universidad dos A ores, rue da Mae de
Deus 58, 9500 Ponta Delgada, A ores, Portugal (Email:;
A. Mota Gomes, Instituto Superior de Educa ~o de Cabo Verde (ISE),
Cape Verde; F. Costa and e E. Correia, Centro de Geografia do
Instituto de Investiga ~o Cientifica de Tropical (IICT), Cape
Verde; Richard Moore, U.S. Geological Survey, Mail Stop 903,
Federal Center Box 25046, Denver, CO 80225 USA (Email:; Frank Trusdell, U.S. Geological
Survey, Hawaiian Volcano Observatory, Hawaii National Park, HI
96718 USA; Veronica Carvalho Martins, U.S. Embassy, Praia, Cape
Verde; United Nations Department of Humanitarian Affairs, Palais
des Nations, CH-1211 Geneva 10, Switzerland; Reuters Information
Services; United Press International; LUSA News Agency, RTP
Internacional Television, Channel 1 Television, and TSF Radio,
Lisbon, Portugal.

Figure 1. Topographic map of Fogo Island showing historical lava
flows (shaded), current lava flows through 11 April (solid), and
selected towns (hatched). Modified from Neumann van Padang and
others, 1967.

Figure 2. Map of Fogo caldera showing lava flows from the current
eruption. Courtesy of Jo~o Gaspar, Universidade dos A ores.