VOLCANOLOGICAL HISTORY OF ISCHIA ISLAND
(Partially based on "Valutazione del Rischio vulcanico
nell'isola d'Ischia"; Laurea Thesis of Massimo Mattera, 1995, Università
degli Studi di Napoli, Italy)
1 - Introduction
Ischia island is located 33 km SW of Napoli (Naples),
Italy. It covers 46.3 km2 and
is the largest island in the gulf of Napoli.
The highest peak of the island is Monte
Epomeosurrounded by several volcanic vents. Mount Epomeo, covers a
surface of 16 km2 or
about the 34.5% of the entire surface of the island. It is almost entirely
made up of volcanic rocks locally called Tufo Verde di Monte Epomeo (Green
Tuff of Mount Epomeo). The top part is covered by sedimentary and volcanic
deposits of younger age (Tufite of Monte Epomeo and Colle Jetto formation).
The central- eastern part of the island is occupied by a triangular-shaped
depression called the Ischia Graben comprised among the villages of
Casamicciola, Barano and Ischia Ponte. The southern border of the graben is
limited by a fault system extending from Carta Romana to Maronti and
to the west by Mount Epomeo. The depression is divided into two halves by a
fault along the valley of Rio Corbore.
The volcanic activity of the island of Ischia is related
to the same causes that produced the volcanic activity along the western
margin of peninsular Italy. About 10 millions year ago the areas now
represented by the italian peninsula and the islands of Corsica, Sardegna
(Sardinia) and Sicilia (Sicily), were bound toghether. A slow anticlockwise
rotation of the italian peninsula separated it from Corsica and Sardegna and
caused the opening of the Thyrrenian sea. The consequent stretching and
thinning of the crust caused deep faults which favoured the formation and
eruption of magmas.
The first modern geological studies of the Island of
Ischia were made by the Swiss volcanologist Alfred Rittmann, who compiled
one of its first geological
2 - Cronology of volcanic activity
The hills bordering Mt Epomeo are old volcanic vents
formed during the last 150000 years. Absolute datings by means of
radioactive methods and volcanological studies permitted to summaryze the
volcanic activity into 5 different cycles. The first two occurred before the
eruption of the Green Tuff which forms most of Mt Epomeo. The last three
phases of activity occurred after the eruption of Mt Epomeo.
- - Phase 1- older than150.000 years
- - Phase 2 - between 150.000 and 75.000 years
- - Phase 3 - between 55.000 and 33.000 years
- - Phase 4 - between 28.500 and 18.000 years
- - Phase 5 - after 10.000 years
The activity before the Green Tuff (Phases 1 and 2)
The products of these phases outcrop mostly in the
southern part of the Island (between Punta della Signora and Carta Romana, Monte
di Vezzi, peninsula of Sant'Angelo, Capo Negro, Punta Chiarito and Punta
Imperatore), in the north western sector (Monte Vico), and eastern part (Castello
d'Ischia). Also the lava flow outcropping at Rione Bocca on the western side
of Epomeo is thought to belong to these phases. The products of the largest
eruption of this period are found at the base of the sequence of Scarrupata
di Barano. Most of these products have been eroded by the action of the
sea and of subsequent explosive eruptions. The result of this activity was
the building of a volcanic edifice probably larger than the present one. A
caldera (a depressed circular structure) was formed after this phase with
the collapse of the central sector of the island. Annular fractures border
the caldera and represent the preferred pathways for the upcoming magmas.
Phase 2 is
characterized by the formation of several scoria cones and domes (Punta
Imperatore, Capo Negro, Punta Chiarito, Sant'Angelo, Punta della Signora,
Capo Grosso, La Guardiola, Monte di Vezzi and Castello
d'Ischia). The dome of Monte Vezzi emitted two viscous lava flows. Other
lava flows form the peninsula of San Pancrazio, Punta della Cannuccia and
Parata. Also Monte Vico belongs to this phase. After this activity there was
a long period of quiscence until 55000 years.
The volcanic activity starts again at 55000 years with
numerous explosive eruptions whose
produts are called
Pignatiello Formation, Green Tuff of Monte Epomeo and Citara formation.The
eruptive vents are no more identified. The possible vent of the Green Tuff
eruption is possibly located in the southern part of the island, between
Sant'Angelo and Maronti. Part of the products of this eruption filled the
pre-existing caldera and covered the eastern part of the island. The green
colour, typical of marine alteration of volcanic products, suggest that the
the caldera was already submerged and lately subsided more as a result of
the eruption. The products of this eruption outside the caldera (Monte Vico,
Punta Imperatore and Scarrupata di Barano) were deposited in a typical
sub-aerial environment. The Green Tuff of Monte Epomeo remained below sea
level until 28000 years ago. At this time most of the Epomeo was raised by
the intrusion of magma at shallow depth. The eruption of the sequence called
Citara Tuffs occurs between 44000 and 33000 years. These products were
erupted during at least three separate eruptions with a typical
phreato-magmatic activity (explosive interaction between magma and sea
water). The Citara Tuffs overlie the Green Tuff at Monte Vico, and between
Capo Negro and Punta Chiarito and at Punta Imperatore.
The first products of this phase are the lava domes of
Grotta del Mavone. The subsequent activity is characterized by thick lava
flows and scorias emitted by the vents of Pilaro. Then there were eruptions
of scoria and pumices found at Scarrupo di Panza. After this activity there
is a phase of quiescence
Numerous eruptions occured around 10.000 years ago and
the volcanic activity continued until the eruption of Arso in 1302 AD. Most
of the eruptive centers are located along the eastern border of Epomeo in
the area called the Ischia Graben. It is possible that these eruptions were
fed by the magma rising along the fractures that borders the Epomeo. During
this phase were formed Monte
Rotaro, Montagnone, Monte Moschiata, Vateliero, Molara and Cava Nocelle.
3 - Mount Epomeo
Mount Epomeo is interpreted as an entire raised block
(volcanic horst). The uplift is dated between 33000 and 28000 years ago, and
was possibly due to the intrusion of magma at shallow depth. The pressure
increase caused the formation of fractures representing the sliding planes
along which the block was raised. The uplifting block was tilted to the
south as a result of a differential movement, and, as a consequence, the
northern side was raised more than the southern side.On the northern side
there are several fractures feeding the thermal springs of Casamicciola and
La Rita and a lineament of fumaroles along a fracture cutting Monte Cito.
The southern part of Epomeo was raised less and was more affected by a
sequence of landslide and mudflows occurring along the inclined surface of
4 - Fumaroles and thermal springs
The volcanic nature of the island is well evidenced by
the presence of fumaroles and thermal springs, that have been since long
exploited as a terapeutical and touristic attraction. The fractures
bordering Mount Epomeo are the preferred pathway for the uprisings volcanic
gases that provide the heat to raise the temperature of the water table.
Fumaroles with temperature near 100 °C are found on the flank of Monte Nuovo
and Monte Cito and along the Maronti coast. In other areas (San Michele,
Monte Rotaro, Fundera e Scarrupo di Panza), the temperature of the fumaroles
does not exceed 46 °C.
The hot springs have temperatures between 20° and 80°C.
They are located at Forio in località Monterone (Castaldi and Castiglioni
springs), at Casamicciola ( La Rita and Bagni springs), at Barano in
località Maronti (springs of Cava Scura, Olmitello and Cava Fredda), and the
springs of Cartaromana, Punta Chiarito, Bagnitiello, San Montano and Porto
d'Ischia. The areas where the thermal springs are localized ,can be
considered as possible sites for future euptions. A fumarolic field called
Solonaria, exploited for the extraction of sulphur, was located in the area
where opened the vent of the Arso eruption of 1302. Deep wells drilled in
all the island provide the evidence of temperature at depth as high as 200
°C and the occurrence of different water tables heated by geothermal fluids
probably coming from a depth of about 3000 m.
5 - Eruptions and earthquakes of pre-historical and
The natural history of Ischia island has been
characterized, since long time, by natural catastrophes caused by eruptions
and earthquakes. A pre-historical site of iron-age is buried under the ashes
of an eruption occurred in the area between Ischia Porto and Casamicciola.
The first greek colony of southern Italy (called Pithecusa) was settled in
Ischia in the VIII century BC. The greek colonists arrived around 770 BC
from Eubea and settled on the Promontory of Mount Vico at the north-western
side of the island. Earthquakes and eruptions compelled the colonists to
leave the island and settle on the coast of Campania where they founded the
colony of Cuma which caused the economic decline of the island. Around 600
BC, the eruption of Monte Rotaro caused the final decline of the colony in
Ischia. In 476 BC the island is occupied by the Syracusans, which were
driven off the island by a new eruption occurred between 474 and 470 BC.
This eruption possibly occured where now is sited the Porto d'Ischia. After
some time the island was occupied again by colonists coming from Naples
(possibly the same that left the island before).
Volcanic activity occurred also during roman time. There
are evidences of an eruption occurred in 91 BC and another one during the
emperorship of Augustus who gave back the island to the neapolitans and got
in change Capri! There are other evidences of eruptions under the emperors
Titus, Antoninus and Diocletian.
The last eruption occurred in 1302 when a vent opened in
the area of Flaiano and emitted a lava flow which lasted for two months. The
lava flow is between 500 and 100 m wide and is presently called Arso (once
it was called "Le Cremate"). It reached the beach between Porto d'Ischia and
Ischia Ponte and destroyed the old village of Geronda. The eruption caused
much panic and compelled the escape of many people to the nearby islands and
continental coast. Since then, the only volcanic activity are the fumarolic
emissions all over the island.
Numerous detructive earthquakes occurred on the Island.
In the last period we recall those of 1881 and 1883. The quake of 1881 was
felt for 7 seconds and had an highr intensity in the territory of
Casamicciola. There were 129 casualties (124 in Casamicciola and 5 in Lacco
Ameno). The wounded were 100 in Casamicciola. 290 buildings were destroyed
in Casamicciola and 159 were damaged. In Lacco Ameno there was the
destruction of 194 buildings (among these the church of S.Giuseppe al Fango).
Also most of the buildings of Forio were damaged.
The earthquake of 28 July 1883 was felt for 16 seconds
and was localyzed in Casamicciola where there were 1784 casualties over 4300
inhabitants. 448 people were wounded. Of the 672 buildings of the village,
572 collapsed and 134 were damaged. In Lacco Ameno there were 146 dead and
93 wounded over 1800 inhabitants. 269 buildings collapsed and 102 were
damaged out of 389. The church of Santa maria del Rosario was destroyed. In
Forio there were 345 casualties and 190 wounded , out of 6800
inhabitants.1344 buildings were destroyed and 977 damaged out of a total
2713. The church of S. Sebastiano also was destroyed. At Serrara-Fontana
there were 28 dead and 21 wounded . At Barano there were 10 dead and 10
wounded. At Ischia the quake was barely felt and a few buildings were
damaged. The quake caused a total of 2313 casualties.
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B i b l i o g r a p h y
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dell'ultima eruzione storica dell'isola d'Ischia: la colata dell'Arso -
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Alpi Centrali, CNR, Milano.
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block resurgence in caldera depressions. A model from Pantelleria and
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Geologia. Boll. Serv. Geol. Ital., pp. 101. Rossi P.L., 1984. Contributi
al rilevamento geologico in aree vulcaniche, Pitagora Editore, Bologna,
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Quad. Ric. Sci. 114 (10) : pp. 133.
Modified 28-October 97