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Crater Poas
Vulcan Poas – one of the most active stratovulkan of the Cordilleras located in the territory of Costa Rica and rising by height of 2708 m. The main crater Poas (1.3 km in the diameter and 300 meters in depth) gave the name to all volcanic array.
Since 1828 when here began to make regular observations, by 2018 the volcano showed activity more than 40 times.
Geomorphology
At top three main structures are located: the main crater Poas, a lagoon of Botos or Cold and Von Franzius's cone, and all of them are limited to breaks which form the volcano-tectonic hollow (graben).
From the middle of the 1960th years till April, 2017 in the main crater four morphogenetic units were selected:
- east plateau,
- kratichesky lagoon,
- dome of a lava and
- internal beach.
The dome which was destroyed on the night of April 19, 2017 was located in the northern sector of a crater (height of 30 m) and had the subpolusharny morphology subject to erosive processes and eruptivny activity.
Walls of the main crater have steep slopes (subvertical in a northern part), also subject erosion of storm drains and landslides. East plateau forms a big volcanic terrace 500 meters long.
On the western flank of a crater the initial morphology of a volcano was changed, for 2018 the structural forms resulting from exhumation of the old issue channels or flues called by volcanic dams which are in turn cut up by breaks are formed.
Geology
Poas's geology, as well as other great Costa Rican stratovulkan, has difficult polygenetic history. Ancient stratovulkan consists of the alternating layers of the lava flows and pyroclastic breeds covered with the dense sequence of the explosive products coming both from Poas's eruptions, and from eruptions of his neighbor, a volcano Barva. This sequence of eruptions can be observed when cutting roads which conduct from Varablanka in New to Hinn.
Around a crater there is a large amount of sulfur in the form of microscopic particles or in the form of the big mass of crystalline aggregates and more ancient lake deposits that indicates that lagoons from thermomineral craters were present at least during the millennium. Lavas in general are andesites and basalt andesites and to a lesser extent dacites and basalts.
Eruptions
Results of a research of scientists showed that the volcano began the vigorous activity about 10-11 million years ago, throwing up fiery flows of a lava and ashes.
The last significant eruption Poas happened in 1910 when about one million tons of ashes were thrown out in the form of a column of smoke and steam.
On May 17, 1953 there took place eruption Poas with whom the activity cycle which lasted till 1956 began. At least two persons were gone.
In 1989 temperature fumarol reaches 900 °C.
In January, 2009 Poas was located in close proximity to epicenter of an earthquake measuring 6.1 which affected including the capital of the country of San Jose and the central valley. More than 40 people died.
In 2009 landslides and small freatichesky (from Greek phrear, phreat - "source") explosions at which the heated magma comes into contact with a large amount of ice or water were also recorded. At the same time there is a flash-like evaporation leading to thermal explosion at which there is an emission of stones, ashes and lava bombs.
Volcanic eruptions Poas often are followed by geyzeropodobny splashes of water of the lake.
More than 60 years Poas was not thrown up, but in 2014 eruptions were resumed: Poas made 60 steam eruptions which varied from small splashes before powerful emissions of ballistic splinters, of water and pair on distance over 400 meters[1].
In June, 2016 vigorous geothermal activity is mentioned. Tremors are connected with tension in rocky breeds caused by the movement of water, magma and gases. In the report submitted by volcanists it is noted that in the southern part of the kraterny lake Poasa there is a temperature increase of water[2].
At the beginning of April, 2017 the group of researchers recorded small steam (freatichesky) explosions on a lake crater. Besides scientists record growth of temperature and also the increased amount of the gas which is thrown out by a volcano. As a result of a sharp gas blowout the lake in a crater of a volcano began to change the color.
On April 14, 2017 two eruptions and 7:57 a.m. led at 7:39 a.m. to emission of a column of ashes and steam three kilometers high.
On April 16 eruptions repeated. In addition the beginning of activity of Poas led to destruction of a dome of its crater. On April 22 after powerful explosion the heated stones scattered on the large territory, having damaged buildings of the park and infrastructure facilities. Scientists noted, a large amount of the heated materials from what follows that to the Earth's surface magma continues to rise.
On February 11, 2019 at night at 1:50 a.m. eruption with a column of ashes 200 meters high began.
On September 23, 2019 emissions of water and steam.
On September 30 at 5:41 a.m. eruption with a column of 2 km of ashes and firm objects.
Hot lake, acid rains and fogs
The lake is known under the name Laguna Caliente (a hot lagoon) and is located in a crater at the height of 2300 meters above sea level. Width about 300 meters, depth are 30 meters.
It is one of the most acid lakes in the world. The acidity varies after rains and changes depending on volcanic activity, sometimes reaching nearly 0 pH. In it is not present or there is almost no life. The bottom of the lake is covered with liquid sulfur.
Water from the lake constantly filters through cracks in the heated rock, evaporating also forming cavities about steam. When pressure in these cavities exceeds the weight of water, steam breaks in geysers which rise by height up to 250 meters.
Acid gases become the reason of acid rains and acid fogs which do harm to the environment, irritation of eyes and lungs.
Vulcan Poas represents an excellent, though extreme example of impact of acid rains. Around a caldera and throughout several kilometers down wind vegetation sickly, brown and black from the spoiled moisture which is besieged from clouds about top.
Many years travelers came to a crater Poas to admire the turquoise acid lake. However in the summer of 2017 the picturesque reservoir disappeared. After that in a crater it was possible to see a small geyser.
Later the lake was again filled.
Observations and researches
Monitoring of emissions of CO2 and SO2
Poas is one of 9 volcanoes included in monitoring of the scientific Deep Earth Carbon Degassing project (DECADE) which problem is collection of data on carbon dioxide emissions (a carbon dioxide gas, CO2) and sulfur oxide (SO2, one of principal components of volcanic gases).
Search of ways of forecasting of steam eruptions: growth of selection of SO2 precedes explosions
And killing freatichesky (steam) eruptions most of which often happen without warning are considered as the most unpredictable. Long time was considered that volcanic activity of this kind cannot be predicted. However the volcano research Poas (results were published in 2016) allowed scientists to come to forecasting a little.
The initial research purpose of Poas consisted in determination of volumes of the gas flows radiated from numerous cracks. On the basis of data retrieveds specialists of Deep Carbon Observatory together with scientists of the New Mexico University, Department of planetary sciences and some other organizations came to a conclusion that prediction of freatichesky explosions nevertheless is possible.
Until recently most of experts believed that steam eruptions are generated by changes in the hydrothermal systems of volcanoes. At the research Poasa it was succeeded to establish that freatichesky explosions are preceded by short-term changes as a part of gas mixes at which the ratio of these or those elements changes.
As a result of 2-month measurements specialists could establish that just before steam eruption in gas mixes sulfur dioxide prevails. Similar outputs indicate that monitoring of composition of the thrown-out gases can become an effective remedy in forecasting of freatichesky explosions and, perhaps, to save lives of many people.
Craters of Botos and Von-Franzuis
Two other craters – Botos and Von-Franzuis – represent the sleeping volcanoes.
The crater of a volcano of Botos (the last eruption in 7500 g BC) overgrew magnificent vegetation and is filled with the lake with green water which has diameter of 370 m and depth of 14 m. Temperature of lake water sticks around +13 … to +14 °C. This water has the increased acidity.
National park
Three volcanic craters are united in national park Vulcan Poas which enjoys wide popularity at tourists.
The nature protection territory was formed by the decision of the government of the country in 1971. For 2018 the territory of the park covers 65 km ².
Fertile volcanic soils define richness of local flora. On the protected area magnolias and several types of orchids grow.
The great number of exotic birds – Gray's thrushes, yarkookrashenny kvezal, toucans, flycatchers and a humming-bird lives in tropical forests. In national park it is possible to meet rare species of squirrels, coyotes, nosukh, skunks and battleships. From natural sights in the neighborhood of Poas the picturesque La Paz falls are located.
Visit by tourists
The crater Poas is called one of the most extreme places on Earth. At the same time, by data for 2014 when Poas made 60 steam eruptions which varied from small splashes before powerful emissions of ballistic splinters, of water and steam on distance over 400 meters, a volcano were visited by more than 200,000 people[2].
Volcanic eruptions Poas happened in April and June, 2017 then the park was closed within nearly 17 months with security perimeter of 2.5 km around a crater. On September 1, 2018 access was open again.
Earlier visitors had an opportunity to go down in a crater Poas, to observe a steam-out, water splashes on height in hundreds of meters, but for January, 2020 it is possible to look at a crater only from far away from the observation deck, remaining on it no more than 20 minutes.
When in an active crater there is an emission of poisonous gases, a volcano Poas close for tourists.
Visit of a volcano by rules requires a preliminary reservation and purchase of tickets at this time:
- It is necessary to be registered in the SINAC system (Sistema Nacional de Áreas de Conservación)
- purchase tickets ($15 for foreigners)
Poas is above the line of frosts, and on a surface of a volcano subzero temperatures are possible. Almost permanent winds and moisture promote the penetrating cold on a caldera. When the clear sky, skin of white tourists burns down under the tropical sun in the rarefied mountain air in a few minutes.
Cost of the parking of a car of ¢2000 (~ $3.50).
The park works from 8 a.m. till 2 p.m.
Visit of a volcano is possible only in groups (to 50 people) which depart each 20 minutes, with 6 guides and takes 45 minutes, including:
- 5 minutes on demonstration of the tickets purchased in advance, signing of paper about a disclaimer
- 10 minutes pedestrian rise on the observation deck
- 20 minutes on the platform
- 10 minutes descent.
Risks for health and life
Signing the papers connected with failure of the park from responsibility you agree with risks, namely:
This activity is integrated to risks for human health.
Increase in concentration of some gases of volcanic origin in air, such as sulphurous gas, sulfuric acid, hydrochloric acid and a carbon dioxide gas, can be sudden or gradual, depending on the direction of wind. In this case impact on health is shown in a type: respiratory problems, conjunctivitis, allergy, asthma, and at too high concentrations they can cause respiratory standstill and death.
Loss of ashes is also connected with the direction of wind. In this case impact on health is shown in a type: respiratory problems, allergic rhinitis, sore throat, cough, asthma, conjunctivitis and irritation of skin. Falling of more coarse particles (rocks of the different size from millimeters to centimeters), depending on height of eruptions and the direction of wind which can cause injuries generally of the head, shoulders and a back and even death from falling and blow of these hardened splinters at a high speed.
For an input in this zone it is recommended to use protective materials, including: a mask of N95 type, goggles, long and thick fibrous trousers and a shirt and also to carry with itself drinking water.
Sulfur oxide influence on the environment and human health
Main article: Sulfur oxide (sulphurous gas, dioxide of sulfur, SO2)
Incidents
At the beginning of April, 2017 in the territory of a volcano there was a tourist group which because of the increased danger had to be evacuated. As a result of Poas's activity some of tourists suffered. At someone doctors stated irritation of eyes, and someone had problems with a throat. As physicians say, all this consequence of impact on a human body of volcanic gases.
Forecasts of volcanic activity
According to forecasts of 2018 in the short term the obvious danger is constituted by acid rains and also freatichesky eruptions which can be not so moderate, as this and last century. Ashes loss, moderate seismicity, lahars (mud flows) and pyroclastic waves are possible. As the top is cut through by several breaks, earthquakes of average force are possible. More significant explosive eruptions, flows of a lava and pyroclastic flows can happen in a long term.
Plans of creation of geothermal stations
For 2019 the authorities of Costa Rica develop plans of creation of hi-tech geothermal stations.
See Also
Notes
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