Volcano

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Volcano
Last eruption of the Vulcano in 1890

Last eruption of the Vulcano in 1890

height 499  m slm
location Aeolian Islands , north of Sicily , Italy
Coordinates 38 ° 23 '28 "  N , 14 ° 58' 46"  E Coordinates: 38 ° 23 '28 "  N , 14 ° 58' 46"  E
Vulcano (Sicily)
Volcano
Type Stratovolcano
Last eruption 1890

Vulcano is an island in the Aeolian Islands in the Tyrrhenian Sea off the north coast of Sicily .

The current word for volcano is derived from the name of the island . In Roman mythology, the island was considered the forge of Vulcanus , the Roman god of fire.

Dates and location

At 21.2 km², Vulcano is the third largest and southernmost of the Aeolian Islands with a distance of around 20 km to the north coast of Sicily. At the 2001 census, the island had 715 inhabitants. The largest town is Vulcano Porto with 361 inhabitants, followed by Vulcano Piano with 287 and Vulcanello with 49 inhabitants. The main source of income for the permanent residents is tourism .

The island belongs to the municipality of Lipari in the metropolitan city of Messina . The zip code is 98050, the telephone code 090. Immediately to the north, only separated by an approximately 800 m wide and 40 m deep channel, lies the main island of the Lipari, the island of Lipari, which gives the entire archipelago its name.

Panoramic view from the Gran Cratere
Fumaroles at the edge of the crater - on the horizon (from left) Filicudi, Salina, Lipari, Panarea and Stromboli

geology

Vulcano consists of four morphological and geological units:

  1. Alt-Vulcano is formed from the oldest volcano on the island, a large stratovolcano that takes up more than two thirds of the island's area - the entire southern part - and the younger piano caldera embedded in it, which is now 300 to 400 m above sea level Plateau. At its eastern edge is Monte Aria , at approx. 500 m the highest point on the island.
  2. The Lentia complex occupies the north-west coast of the island and is a small stratovolcano that has grown together from volcanic dome .
  3. Within the Lentia volcano, the active volcano, the 391 m high Fossa , which is now in the so-called fumarole stage , was formed in the last 10,000 years .
  4. The flat lava plateau of Vulcanello emerged as the northern appendage of Vulcano in historical times. Vulcanello consists of three nested volcanic cones.
Crater of the fossa from the west

The fossa has operated at intervals of varying length since ancient times. Ancient writers, above all Thucydides (5th century BC), report of moderate but regular activity, so that Vulcano was probably better known than Stromboli in ancient times.

In the 5th century BC BC, an exact date has not been established, a violent eruption probably took place, the thunder of which was audible in large parts of Sicily . By the year 126 BC BC, in which the lava plateau of Vulcanello was formed, there seems to have been no major eruptions on the island. The three cones of Vulcanello emerged until around the middle of the 6th century AD. Up until that time, the fossa has been shown to be inactive. It was not until the second half of the 6th century that the fossa began to operate again, with Fossa II, also called Jungfossa, whose pumice ashes can also be found on Lipari. Around 1727 the upper northern side crater, the Forgia Vecchia superiore, was blasted out and was apparently active for several years.

1731 began a new violent eruption phase with the formation of the southern smaller secondary crater (Forgia Vecchia inferiore). In 1739 the activity ended with the outflow of the Pietre Cotte obsidian flow . From this eruption phase it is documented that their ashes also fell on Lipari, Salina and Stromboli and that houses on the north coast of Sicily collapsed and people were killed by strong earthquakes .

Other violent eruptions have been reported from the years 1771 and 1783.

The eruption from 1888 to 1890

In January 1886 a violent phreatic eruption began with the ejection of blocks and ash. Then it seemed to be calm again. If you stood at the edge of the crater, “you could hear a continuous rolling, as if a train was passing over a bridge” ( Mercalli 1888). Fissures in the crater wall, from which gases escaped under strong pressure, were often red-hot, in the dark one could see bluish and green-lined flames from the hydrogen sulfide ignited in the air and the glowing boric acid vapors.

Fumarole

At the beginning of August 1888, the fumarole activity increased and the temperature of the vapors finally increased so that the sulfur liquefied and partially self-ignited. The convicts used in sulfur mining refused to descend into the crater.

On the night of August 3, 1888, the last eruption so far began with an explosion, which was quickly followed by others that grew in intensity. Ashes and large glowing boulders fell up to 3 km away on the inhabited northern part of the island. They broke through the roofs of the factory and residential buildings and set fire to the sulfur stores and some of the ships lying on the pier. When the gorse vegetation of the cone went up in flames, the Lipariot believed that a lava flow had flowed onto Vulcano. The few inhabitants of Vulcano had saved themselves with boats, the convicts could only get to safety in the alum caves of Faraglione.

On August 5th, the situation was quiet again, but this was ended by new violent eruptions on August 18th. A particularly violent eruption occurred on March 15, 1890, with breadcrust bombs weighing tons and up to 5 m in diameter falling. The explosive activity did not end until March 22, 1890.

The Italian government sent a commission formed to study these eruptions, a volcanological pioneering act. The volcanologist Giuseppe Mercalli coined the term " Vulcanian Eruption " based on his observations of this series of eruptions .

The "Dead Field"

The dead field and the sea heated by submarine fumaroles with bathers

The 37,000 m² area between the Fossa and the Vulcanello is known as the “Dead Field”. A wide variety of fumarole activities on land, on the beach and in shallow water can be observed up to a depth of 18 meters. The fumarole zone in the water runs parallel to the coast and is 500 m long and 100 m wide. The Dead Field owes its name to the expansion of activity in the years 1913 to 1916. Any plants present here had to give way to the heat and poisonous gases.

There are three larger fumarole areas, but there are also several small fumaroles whose vapors are not noticed in dry and hot weather. You can, however, by lighting z. B. a cigarette introduce fine particles that act as condensation nuclei and thus cause an increase in the condensation of the water, which is noticeable in clouds of vapor. This is known as the "solfatara phenomenon".

In quantitative terms, water vapor dominates the gas component. If one only looks at the “dry gases”, CO 2 and hydrogen sulphide (H 2 S) predominate in terms of quantity . The gas emissions are estimated at around 5000 m³ per hour.

Due to an average temperature of around 100 ° C, the fumaroles are called cool. The fumaroles produce minerals such as B. gypsum , sulfur , salmiak or sassolin .

In the so-called "oxidic environment", hydrogen sulfide reacts with oxygen to form elemental sulfur. However, this oxidation process only happens up to the groundwater level or in places where the water is very oxygenated. Here, sulfur milk either turns gray-yellow sludge or it is granularly crystallized or recrystallized. SO 2 is formed on the surface , which reacts with water to form sulphurous acid . The oxidation that now follows produces sulfuric acid . This breaks down the sediments to great depths and releases iron , which then ends up in the groundwater . There it reacts with H₂S and forms iron sulfides . Thus, the statement can be made that the iron content (6.5% in the sand) is of volcanic origin.

The large pore volume of the sand (originally 35%) favors the separation of iron sulfides. Iron pebbles are formed in three forms . Two of them are pyrites, which differ in their structure and size. The third form of training is marcasite . These types of training are dependent on the pH value and the temperature of the water.

There is a solidified sulphide layer at the height of the water table. Due to fluctuations in the groundwater level, oxidation creates a thin brown iron zone, also known as the “ iron hat ”.

Thus, the normal profile of the dead field in the area of ​​fumaroles consists of three zones:

  1. Firstly, from a sulphate zone that is 50 cm thick and consists of a hard crust of plaster of paris, alum, etc. in the upper part.
  2. Second, from a 1.3 m thick sulfur zone, consisting of crystalline sulfur and
  3. thirdly, from an ore zone, which consists either of a 10 cm thick limonite layer or a renewed sulphide layer from the above-mentioned pyrites or marcasites.

In the shallow water area, where the gases flow directly into the sea water, the hydrogen sulphide is neither converted to free sulfur nor to sulphates due to a lack of oxygen.

Useful products of the fumarol activities are sulfur, boric acid and alum , which is obtained from alunite . The latter was used for tanning hides and as a stain in fabric dyeing.

Any attempts to use the steam sources to generate energy failed because of borehole eruptions.

There is also a groundwater sludge pool within the Dead Field, which has temperatures of 35 to 52 ° C due to the hot gases. It is hoped that bathing in the mud will heal skin diseases , rheumatism and arthritis .

hazards

The health hazards of the rising gas in the mud pool should not be neglected. In addition to CO 2 and other gases , the escaping volcanic gas contains around 1% H 2 S (hydrogen sulphide). The toxicity of the gas is already considerable in the ppm range. The gas is quickly diluted with air by the wind, but the H 2 S concentration of the air above the pond surface can reach values ​​in the two to three-digit ppm range (measuring system: op-TDL; measuring height: 30 cm above the pond surface; Wind ~ 1 m / s). The dilution effect can be weakened by the hollow position of the pool and no longer be sufficient when there is no wind. Almost no “water exchange” takes place in the fango pool, so that organic substances of anthropogenic origin collect in it (urine, skin flakes, hair, etc.). It is not advisable to take a bath in the fango pool; if you still want to do it, you should at least make sure there is enough wind.

Inhaling volcanic gases generally poses a considerable risk. This applies in particular to the crater area, where large amounts of gas escape. Depending on the weather, the gas may not be visible through its vapor clouds. A descent into the crater funnel can be fatal due to the higher concentration of toxic gases there, depending on the wind strength.

The steam plumes consist, among other things, of strongly corrosive acids. Stainless steels can also be attacked quickly if they come into contact with the steam.

Another danger comes from the high temperature of the escaping gases. Temperatures around 400 ° C on the surface of some fumaroles in the crater area are not uncommon. The “hot” fumaroles can be recognized by their gray appearance, as no sulfur crystals are deposited here. Occasionally, molten sulfur can be seen in these “hot” fumaroles.

traffic

There is a daily car ferry to Milazzo , there are also (not daily) ferries to Naples . There are connections to the neighboring islands with hydrofoils. In the summer months there is a boat connection from Palermo via Alicudi and Filicudi to Vulcano.

photos

  • General view from Lipari

  • Main crater

  • The slope near the crater

  • Sulfur fumaroles in the crater

literature

Web links

Commons : Vulcano Island  - collection of images, videos and audio files

Individual evidence

  1. ↑ Istat 2001