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Arenal Volcano, Costa Rica

Arenal Volcano lava flow  Majestic colossus that started explosively its great and most recent period of volcanic eruption activity in the morning of 29 July 1968, and keeps it continuously but moderately, as the most active volcano in Costa Rica. Arenal Volcano is fully surrounded by Tropical Rainforest, including its flora and fauna, is accompanied by inactive Chato volcano and the relics of another ancient volcanoes, and have two small lakes of emerald colored water at its laps, as an effect of ancient eruptions and its geologic structure. This creates a really mystical nature experience that attracts a lot of visitors, from tourists while in a Costa Rica vacation, to scientists investigating the manifestations of the Earth power. It had remained by 42 years as one of the current 16 most active volcanoes in the world, with a volcanic eruption several times on a daily basis, including its well known spectacular nocturnal red-hot lava flows. In addition it remains as one of the most observed and studied volcanoes by the international scientific community.

According to the most updated work in the field of some Costa Rican geologists, Arenal age is at least 7,000 years (1) , time in which it had at least 4 great eruptions highly explosive (plinians), was jointly in eruption with the now extinct Chato Volcano, until this last ended its activity about 3,500 years ago, and devastated nearby indigenous settlements several times in the last four millennia.

(En Español: Volcán Arenal)

Arenal Volcano Facts & Information

Arenal Volcano Most Recent 2010 Eruptions Report Arenal Volcano Pictures. Extra Gallery. Last taken at 08/04/2011 11:35:50 am Arenal Volcano Tour. Volcano Eruptions, Activity and Red-Hot Lava View Most Recent 2012 Eruptions & Activity Reportclick!
Most Recent 2011 Arenal Volcano Picturesclick!
Arenal Volcano History
Arenal Volcano Tour
Online data (11): Arenal Volcano online. OVSICORI WebcamArenal Volcano onlineclick! (OVSICORI webcam is out of service)
Location: La Fortuna, San Carlos. Costa Rica.
10°27'48"N, 84°42'12"W
(around 90 km north-west of San José)
First Exploration: In 1937, a 7 people local group climbed up to the top (of the supposed peak) and reported a crater cavity covered with vegetation and featuring fumaroles (a dormant volcano!). (2)
Location Map of Arenal Volcano in Costa Rica Current Activity Period: 42 years of continuous eruption activity from 1968 to 2010.
1968 Eruption Effects: Three new fissural craters (A, B and C) by a strong lateral explosion on the western flank and a deposit of pyroclastic materials. Raised an ash column about 10 km in height and a total area of 15 km² towards W, including 2 villages, were completely devastated. An area of 230 km² was slightly affected by ash fall. (3)
Volcanic Activity: Vulcanian and strombolian eruptions (explosive eruptions) with tephra emission and ejection, lava flows, pyroclastic flows, ash and gases. There is acidic rain near the crater under gas column, noticeable towards NE as well as NW (towards the national park facilities).
Altitude: 1,720 m ASL (5,643 feet). (4)
Volume: 10-12 km³ approx. (it has been produced 0,7 km³ since the 1968 eruption). (5)
Age: More than 7,000 years (radiocarbon measure on the most up-to-date earliest volcanic eruption evidence) (1)
Volcano Type: Stratovolcano (built by strata of fine material, as the ash and pyroclasts, alternated with strata of solidified lava or volcanic rocks).
Craters: Active crater (C) and "inactive" (D). Both of about 100 m of diameter.
Volcanic Rock Type: Mainly Basaltic Andesite (54,6 weight% of silica, of dark gray color with cristals of plagioclase, augite and olivine).
Geologic Origin & Nature: Arenal Volcano is part of the Pacific Ring of Fire, and originates by the rising of magma through the earth's crust, which is upper mantle melted by the subduction of the Cocos tectonic plate under the Caribbean plate, process which also incorporates oceanic water and yields it a resultant chemical composition and viscosity, all of which impart an explosive behaviour to the eruptions.
Geographical surroundings: The Tropical Rainforest (habitat of the Jaguar, Tapir, Peccary, Howler Monkey, Blue Morpho Butterfly and Poison Dart Frog among others), Arenal Biological Reserve, Arenal Volcano National Park, Monteverde, Children's Eternal Rainforest, "Los Perdidos" mountains, Chato Volcano (inactive), La Fortuna Waterfall, Hot Springs, Tabacón thermal river, volcanic originated small lakes, Lake Arenal, Venado Cave, La Fortuna village and El Castillo neighbourhood.
To catch it clear: At dawn it is frequently clear and highlighted by the first sunlight beams, which allows for extraordinary pictures.
*Arenal Volcano eruption activity appreciation is possible with properly safety guidelines applied by tour operator guides and Arenal Volcano National Park authorities, so follow it carefully.

Picture of Arenal Volcano eruption of 24 May 2010, one of the pyroclastic flows emitted towards SW flank.
(05/24/2010 12:09:01 pm, Víctor Hugo Quesada, Arenal Eco Zoo, El Castillo, San Carlos).
Picture with zoom of eruption of 24 May 2010, front of pyroclastic flow emitted towards SW flank.
(05/24/2010 12:08:48 pm, Víctor Hugo Quesada, Arenal Eco Zoo, El Castillo, San Carlos).
Arenal Volcano 2 hours after previous picture of eruption of 24 May 2010. Note the light trace left from top to the base.
(05/24/2010 02:02:54 pm, Olger Aragón, Foto Koky, La Fortuna de San Carlos).
Zoom from SW flank of crater of Arenal Volcano; there were about 15 pyroclastic flows at 24 May 2010. Note the ditch left.
(05/24/2010 02:06:09 pm, Olger Aragón, Foto Koky, La Fortuna de San Carlos).
Spectacular nocturnal vew of red-hot lava flow along SW flank, 3 days after pyroclastic avalanches of May 24.
(05/27/2010 11:36:04 pm, Olger Aragón, Foto Koky, La Fortuna de San Carlos).
View of a pyroclastic flow deposit emited toward S flank.
(03/2010, Jorge Barquero, OVSICORI).
Lava flow throughout S flank of Arenal Volcano, which is the main activity still in March 2010.
(24/02/2010, Federico Chavarría, OVSICORI).
Zoom of the lava flow throughout S flank of Arenal Volcano; the main activity still in March 2010.
(24/02/2010, Federico Chavarría, OVSICORI).
Arenal Volcano pyroclastic flow throughout SW flank due to collapse of a lava flow front, sighted from a point near the ARE-1 seismological station. (07/07/2009 11:20 pm, Luis Madrigal, RSN). Deposit of volcanic rocks after the pyroclastic flow of July 7 throughout SW flank.
(07/07/2009 2:00 pm, Luis Madrigal, RSN).
Flank S of Arenal Volcano, dotted lines shows the maximum width of detachments happened at June 16, 2009. The yellow arrow shows the maximum reach of materials, 800 m above sea level.
(06/17/2009 12:30 pm, T. Marino, OVSICORI).
At last! a recent great Arenal Volcano strombolian eruption picture, despite the cloudy top (09/09/2008 11:45:12 pm). Zoom of the previous Arenal Volcano strombolian eruption picture. The top is cloudy. (09/09/2008 11:45:12 pm). Arenal Volcano keeps continuously throwing red-hot lava as you can witness at nocturnal volcano tour (09/10/2008 06:40:43 pm). Arenal Volcano activity is highlighted by the moon (09/08/2008 09:27:32 pm). Dream-like mystical splendor of Arenal Volcano activity highlighted by the moon (09/08/2008 11:21:19 pm). Arenal Volcano view, just after dawn; note the yellowish coloration by acidic rain (09/02/2008 06:14:19 am). Volcano double top zoom from previous view; note the yellowish vegetation by acidic rain (09/02/2008 06:14:28 am). Arenal Volcano active crater (09/02/2008 06:14:28 am). Arenal Volcano inactive crater, strongly eroded and some yellowed vegetation by acidic rain (09/02/2008 06:14:28 am). Arenal Volcano is surrounded by lush tropical rainforest (09/19/2008 03:29:14 p.m.). Impressive Arenal Volcano as viewed from the observatory point (09/19/2008 04:01:42 pm). Arenal Volcano crater at June 08, 2008 (Courtesy of OVSICORI). Arenal Volcano, SW flank pyroclastic flow at 7:23 am, June 10, 2008 (OVSICORI). Arenal Volcano pyroclastic flow eruption at 7:26 am, June 10, 2008 (OVSICORI). Lava and detachment area of avalanche in June 10, 2008 (OVSICORI). SW flank Arenal Volcano eruption at 7:37 am, June 10, 2008 (OVSICORI). SW flank pyroclastic flow at 7:39 am, June 10, 2008 (OVSICORI). 130mx200m materials deposit from recent eruption. June 11, 2008 (OVSICORI field work). Pyroclastic flow layers seen in situ at June 11, 2008 (OVSICORI field work). In situ pyroclastic flow deposits seen at June 11, 2008 (OVSICORI field work). SW flank gutter by recent eruption, as seen in situ at June 11, 2008 (OVSICORI field work). Arenal volcanic activity seen in situ at June 11, 2008 (OVSICORI field work). Arenal Volcano spectacular eruption at Vantage Point. Arenal Volcano spectacular eruption view near National Park. Unforgettable hotel view: Stars from sky witness Arenal Volcano red-hot lava eruption... A close nocturnal view of lava eruption from Arenal Volcano! Closest view of the red-hot lava of nocturnal volcanic eruption!
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Current image: Arenal Volcano online. OVSICORI WebcamArenal Volcano onlineclick! (OVSICORI webcam is out of service)


History

Origin, Formation and Ancient Eruptions

 With a double cone shape, well defined, Arenal Volcano is the youngest volcano in Costa Rica and currently the most active of this country, and one of the most active along the world. The volcanic structure of Arenal is constituted by two superposed cones, which correspond to the original 1,633 m almost perfect shaped cone (the inactive "Arenal Peak"), and the new cone that has been partially superposing to the former, with its continuous material emanation from the active crater that has surpassed its altitude (and the current value is about 1,720 m). Those cones lies very near of the eastern shores of Lake Arenal (a natural lake that has been enlarged with a dam three times its original size by a hydroelectric project in the early 70's). Arenal volcano is located along a volcanic chain formed sometime between 100 and 12 thousands of years ago, and containing in building up chronological order, "Los Perdidos", "Chatito" & "Espina" lava domes; "Cerro Chato" inactive volcano (with 500 m wide and a fantastic lake-filled crater, about 38 thousands of years of antiquity, and one of its ancient lava flows whose erosion and abrupt steepness due to faults had gave place to the beautiful Fortuna Waterfall) and finally the Arenal Volcano, uninterruptedly active at today.

According to the last evidence from the research of Costa Rican geologist experts Gerardo Soto and Guillermo Alvarado, the earliest known eruptions by now of Arenal took place about 7,000 years ago (1) (which establish a minimum age limit); even more, a superior limit of about 20,000 years was defined, below which may reside the maximum age possible, in the case of related future discoveries. Besides, Arenal was active contemporarily with its "partner" Chato Volcano until this last became dormant about 3,500 years ago. The volcanic eruption activity of Arenal, through these seven millennia, has changed within a wide range: from gases emanation, passing by lava effusion periods sustained by years (which gradually have built, stratum by stratum, the well delineated conical silhouette) to explosive eruptions; either of short duration and few volume erupted or very explosive (plinians), with pyroclast columns which had reached the medium layers of the stratosphere (In the last 3,200 years had occurred 4 great plinian eruptions in a cyclic way, at intervals around the 900 years).

 The latest remarkable volcanic eruption stage, previous to the current, was at the Christopher Columbus arrival to original indigenous Costa Rica land. Such event produced the amazing pyroclastic flow deposit, dated around 1525 A.D., that now looks like a hill at the very road side (which is the cause of its curve there) close to the Tabacón river. And this would be witnessed by the indigenous people which inhabited at the cone surroundings, which were devastated in different times by eruptions along the last four millennia, according to the plentiful archaeological digs made in the zone (recently some stone roads highlight as discovered by NASA using remote sensing technology, as antique as 2,500 years ago). After that, has followed about 400 years of dormancy, causing that the cone were locally known as "Cerro Arenal" (Arenal Peak) and not as the true active volcano that is actually. Due to its conspicuous shape of almost perfect cone it generated the impulse in 1937 by which a group of seven local residents be organized by first time (as the historical record shows) to explore its top, where they found, once at a 6 m width border, an huge cavity with the shape of a crater (comparable in size to a football camp), covered with vegetation, but with eight gaps though which gases emanation occurs. In despite of the testimony offered their earnestness was doubted, because of the seeming inactivity perceived from distance and generally accepted. (2)

The Eruption of 1968

But no doubt was left when the most recent volcanic activity period of Arenal began, after a sequence of local earthquakes for several hours, with a major west-directed explosive eruption arising from the western slope of the cone in the morning of 29 July 1968, followed by another similar at 31 of that month, with catastrophic consequences for two small settlements built justly into the devastated area ("Tabacón" and "Pueblo Nuevo", with about 70 deceases reported, and perhaps an unknown number of not reported). La Fortuna village, although at the other side of the volcano, suffered abundantly ash fall and was evacuated as caution. This event equivalent in power to an atomic bomb nuclear explosion, created three new craters, two (denominated B at 1,160 m and C at 1,400 m of altitude, approx.) on the western flank and one at the base of it (A, with 250 m of diameter and about 1,060 m of altitude), being this last the one which caused the major part of the eruptions and destruction of that year. The vegetation, big trees included, was completely removed in the vicinity of the explosion craters, even at 3 km, there were uprooted trees.
A continuous weak explosive activity accompanied by slow lava effusion and the occasional emission of pyroclastic flows has occurred since that date, and consolidated through the higher of the vents (crater C), giving place to the current active crater, totally covering the craters A & B, and surpassing the 1,633 m in altitude of the former cone.

Posterior Eruptions

After its explosive and sudden reactivation Arenal Volcano have had meaningful eruptions surpassing the almost daily manifestations and low magnitude eruptions, those are which have the public attention and are recorded by the news. As example in 28 August 1993 occurred a big pyroclastic flow followed by a big lava flow as a result of the detachment of the NW flank of the crater (which left a "U" shaped cavity at the summit). At April and mainly (with much ash emission) at 5 May 1998 several pyroclastic avalanches took place along the NW flank, towards the Tabacón river. Another eruption with a considerable pyroclastic flow took place 23 August 2000 along the N flank (whose hot gases unfortunately reached three persons hiking into the high risk area, dying the guide and a tourist). Also there was remarkable pyroclastic flows from 24 to 26 March 2001, at 5 September 2003, 6 July 2004, 10 May 2006 and 18 September 2007; through the NW, N, NE, N and SW crater C flanks respectively. In total, in the present eruptive period sustained since 1968, there were produced more than 100 lava flows and more than 60 pyroclastic flow events.


Volcanic Activity

Because of its uninterrupted volcanic eruption activity Arenal Volcano is worthy one of the current most active volcanoes in the world. Such activity is manifested in the following ways:
Gases emanation: Generated at the craters and coming from the interior through the vent or conduit; some of its components, by mixing with water vapour can generate acid rain, which affects the vegetation at the N flank causing its noticeable yellowing. The gas composition includes water vapour (more than 90%), carbon dioxide and sulphur dioxide.
Rumbling: Strong noises from explosions after sudden release of compressed gas by the continuous accumulation, or by the rock rupture of the crust as the magma rises towards the surface.
Earthquakes: produced by the same reasons that rumbling while magma rising. Although their intensities are relatively weak, originate at low deep and their scope is restricted to volcano vicinity, their local effect can be considerable, ranging from those which are only recorded by the continuous monitoring seismometers network (the most), to those which disturbed local people hours before the explosive eruption of 1968. They are not caused nor related to local fails nor tectonic plates. From Arenal seismic monitoring it has been determined that low magnitude seismic events precede pyroclastic flow eruptions.
Hot Springs: Produced as the aquifer groundwater makes contact with rocks heated by the volcano magma, at the superficial spring sources, carry out the absorbed heat and dissolved minerals as well. Its temperature and composition can change according to the volcanic activity. They are intensely used for the local ecotourism because of their relaxing and invigorating properties.
Volcanic Eruptions: Besides just to emanate gases, also are thrown to the exterior solid materials (igneous rocks), which ranges from passive lava effusions, to the explosive and amazing strombolians or the dangerous and sudden pyroclastic flow avalanches.
Cone Grow: Volume and altitude increasing as a result of the accumulation in strata or layers of solid materials thrown by eruptions. This continuous emanation of materials by the crater C had covered the craters A & B, because formed the cone of recent materials (gray colored) which grows superposing to the older one (rainforest covered and with brown color at the exposed top).
Terrain deformation: As a result of the rise and accumulation of materials in the volcano inside, which generate huge pressure towards the exterior, the terrain in the cone slopes and at the base of it becomes swollen or deformed, which is determined and exactly monitored with geodetic technology.
Strata: As a result of ancient eruptions, strata or layers and deposits of thrown materials are being accumulating, which are left underground by the soil or another strata, in a superposed way, being the most deeper generally the older. In the case of Arenal Volcano, its cyclic eruptive history has been recorded and understood thanks to the study of its sequence of strata (layered stratigraphy); indeed, it have been found strata up to 7,000 years in age, by now.

The gas and steam columns which are emitted from volcanoes like Arenal are the external expression of underground solids and fluids. The gas that is produced into the volcano deepness increases its volume as it rises through the porousness and micro-fractures, reaching the atmosphere with high pressure. Gas columns of Arenal ranges in size according to the kind of the respective eruption. In the phases of greatest gas liberation it has been observed columns between 500 m and 1 Km above its top. The major effect of these gases in the first 20 years after its awakening in 1968. At the late 80's the western side (the most affected by acidic rain) retook a natural regeneration process and currently looks green and reestablished. (6)

Volcanic Eruptions

The explosive behaviour of Arenal eruptions is consequence mainly of the presence of oceanic water into the magma, which is introduced in it while in the process of subduction (of Cocos Tectonic Plate under the Caribbean one) that originates all the vulcanism phenomenon in the area.

Arenal Volcano generates or have generated the following kind of eruptions:
Plinian (explosive): Have occurred historically at previous activity periods. It is characterized by great vertical explosions capable of rise rock fragments and a gas and ash column of 20-55 km of height. According to Arenal cyclic eruptive history, it is estimated that the next plinian eruption would occur during the next century (XXII).
Peléan (highly explosive): The destructive eruption of 1968. Sudden explosion by the failure, under increased pressure, of a solidified lava blocking (high viscosity lava) that obstructs the vent. Can generate a column of 1-25 km in height as well as a very powerfull pyroclastic flow known as Nuée Ardente.
Arenal Volcano Pyroclastic Flow Pyroclastic Flow: Is a burning cloud of gases, rocks and particles (pyroclasts) which runs as avalanche down the slope at speeds of 200 km/h or even more faster and with temperatures greater than 500 ºC, hence it devastates all into its scope. Is the most dangerous eruption type.
Arenal Volcano Lava Flow Lava Flow: No explosive effusion of lava, which in the case of Arenal is not fluid but rock fragmented or blocks. Lava effusion periods have succeeded the ancient great plinian eruptions. Lava flows also occurs after pyroclastic avalanches by top materials collapse.
Vulcanian (lowly explosive): Generates great ash amounts. Can generate a column of 1-25 km in height.
Arenal Volcano Strombolian Eruption Strombolian (moderately explosive): the most frequent, throws lava and blocks through the air hundreds and even thousand of meters (the picturesque elliptic paths in the photographs); low ash emission. Can generate columns of 0,1-5 km in height.


At the Arenal Volcano top are being produced small structures called lava domes which are built and destroyed continuously as new magma additions alter it. A lava dome is an accumulation of viscous lava surrounding the exit spot due to the impossibility of immediate displacement. In the case of Arenal, even it has been observed the emanation of lava flows under the heavy dome structures. (7)

Arenal Lava

Lava is magma that have reached the surface and have lost a great amount of the gases contained inside, so it emanates and goes downhill from the vents openings, either the crater or some fissure, as a lava flow, which then remains as deposits of solid rock after it cools and solidifies. Indeed, most of the volcano cone has been raised in this way.
Arenal Volcano lava, along its history, has changed very few in its dynamics, reach, petrology, chemical nature and general mechanical behaviour: andesitic basaltic composition, high viscosity, blocky, and of low velocity. This means that it is not fluid nor liquid as in the case of Hawaii volcanoes, but with paste consistency, almost solid, and presented in the form of blocks (numerous, big and irregular) which roll down, jumping and being fragmented as hitting the irregularities, coming finally to a stable place, where they accumulate Lava block from Arenal Volcano (2x6 m approx.)(either in the flank of volcano, its base or near it). The size of some of the lava blocks reaches such dimensions, that is comparable with a room, or even a entire small house.
After being erupted from volcano the fully red-hot lava is initially at high temperatures (near 1000 ºC), then it cools losing its red glow starting from the exterior and solidifies to become solid rock. Following its rolling down and stabilization, most of these lava blocks start to crack in two or several parts, allowing to see through the fissures the remaining but decreasing internal red-hot incandescence; then each of the parts cracks in more, and soon this generates an amount of fragments and particles, similar to sand (and after this the name Arenal, which means "a lot of sand").


Scientific Monitoring and Research

Arenal Volcano is under permanent study by the Costa Rican scientific authorities: the Área de Amenazas y Auscultación Sismovolcánica, of Instituto Costarricense de Electricidad (ICE); the Observatorio Sismológico y Vulcanológico de Arenal y Miravalles (OSIVAM), Guanacaste; the Red Sismológica Nacional (RSN), at Escuela de Geología of Universidad de Costa Rica, San José; and Observatorio Vulcanológico y Sismológico de Costa Rica (OVSICORI), at Universidad Nacional, Heredia.

Potential Events & Volcanic Hazards

Due to the activity of Arenal Volcano, despite the accustomed local residents, it represents by its nature a potential hazard or problems source in one way or another for social activities and infrastructure, as well as the people themselves. As a product of the scientific work of experts like Gerardo Soto (and some colleagues) the following events and volcanic effects have been identified at Arenal, capable of material and personal damage, which can take place with greater or less probability along the time:
1) Gas discharge, its dispersion by the winds and acid rains.
2) Ballistic bombardment of blocks and bombs (volcanic rocks of considerable size thrown to the air).
3) Fall of pyroclasts carried by the winds.
4) Pyroclastic flows and surges.
5) Opening of new lateral craters and generations of blasts.
6) Blocky lava flows.
7) Lahars originated during or after eruptive periods.
8) Volcanic rockslides and avalanches, because of the collapse of segments of the volcano edifice.
9) Waves generated by avalanches or pyroclastic flows entering the reservoir (Seiches).
10) Volcanic earthquakes (Mercalli scale intensity ≤ 5) generated by the ascent of magma before eruptions.

All of this knowledge allows to be prepared and informed in the occurrence of high magnitude volcanic activity events, and to avoid or minimize in this way the impacts of their destructive effects.


Local Tourism

Arenal Volcano Area Arenal area has evolved from rural and remains under a developing nature oriented tourism. Besides of being an attraction as itself, Arenal Volcano with its effects and the geological forces that originated it have moulded the area in such a way that, joining the local flora and fauna, it results in a convergence zone for different nature manifestations, distinctive along the planet: Chato inactive volcano with its crater lake, hot springs, small lakes at Arenal Volcano base, springs and rivers, Lake Arenal, Venado Cave, waterfalls, the Tropical Rainforest and a extraordinary biodiversity. For all of these reasons was created in 1991 the Arenal Volcano National Park (currently with 12,124 ha), which allow to manage and control the visits and appreciation at the most active side of the volcano, while ensure the protection of a wide area of surrounding wildlife and rain forest (which is the basin that supplies the Arenal hydroelectric system).

The solely impressive background image of the volcanic chain as seen from La Fortuna and the surroundings as well, is enough to recall the place and desire to experience it in detail. And the constant volcanic activity and minimal endangerment at safe distance by Arenal behaviour, makes it a very popular tourist destination that allows the chance to watch an active volcano (which is statistically small along the world). Specially when eruptions occur at night, because the lava and incandescent rocks make a very spectacular sight. When the lava is emanated, its red glow at the crater can be seen from almost any spots in the vicinity of the volcano, even sometimes from La Fortuna village. If during a clear night you have the opportunity to witness them, from some place in total absence of civilization lights (which is easy to have there), this will allow the total splendor of the stars (and the Milky Way inclusive), in conjunction with the red-hot lava volcanic eruptions, so one of the most sublime and unforgettable nature shows will take place.

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Current & Latest Arenal Volcano Eruption Activity Reports

January - May 2012: OVSICORI & RSN Information
Non-Eruptive Minimal Activity: Gases Emission.
The Arenal Volcano remains only with the emission of gases in the crater C and the usual activity in the crater of fumaroles D. It has established and maintained a break in the emission of solid materials (ash, rocks or lava). The seismic monitoring indicates that the internal activity of the volcano so far remains low and the external manifestations have been reduced to a minimum. Throughout all the year 2011 and the beginning of 2012 there has not been registered a eruption, only low gas emissions. For the first time in 42 years of continuous eruptive activity, since about October of 2010, the Arenal Volcano stops producing eruptions in the form of explosions, pyroclastic flows or lava effusion. It is still an active volcano but now is not erupting, for the moment.
Source: Volcanological & Seismological Observatory of Costa Rica (OVSICORI-UNA), National Seismic Network (RSN), local residents at La Fortuna and El Castillo.


Gasses emanation from Arenal Volcano crater C (07/30/2011). August - July 2011: OVSICORI Information
Normal Activity: Gases Emission.
Arenal Volcano, OVSICORI Webcam (08/30/2011) Arenal Volcano remains emitting gasses at a minimum rate from crater C, as well as in the fumaroles at crater D. It remains the temporary pause in the emission of solid materials (rocks and lava). From fieldwork visits (left) and with the webcam monitoring (right) it has been evidenced, in clear conditions, the raising of small gas and steam columns from active crater C.
Source: Volcanological & Seismological Observatory of Costa Rica (OVSICORI-UNA), OVSICORI webcam.


March - June 2011: OVSICORI Information
Normal Activity: Gases Emission.
Arenal Volcano keeps emitting gasses as well as the activity in the fumaroles at crater D. It remains the temporary pause in the emission of solid materials (rocks and lava). The seismic monitoring shows that the internal activity of the volcano remains normal, only the external manifestations had been reduced.
Source: Volcanological & Seismological Observatory of Costa Rica (OVSICORI-UNA), local residents at La Fortuna and El Castillo.


January 2011: OVSICORI Report
Normal Activity: Gases Emission.
Arenal Volcano keeps emitting gasses and a temporary pause in the emission of solid materials (rocks and lava) is taking place. From visits made by OVSICORI geologists, in December 2010 and January 2011 it is verified that gas emission is occurring mainly through the NE vent. Although there are some reports, of sporadic explosions in recent days.
It is occurring recently the temporary stop of the emission of solid materials from the top, which does not mean that the volcano activity is ending, because this is not the only indicator of the dormancy of an active volcano. Besides of the well known visual manifestations of an active volcano (like the lava and the eruptions), also are important the seismic signals, as well as the temperature and geochemical composition of the hot springs waters. Indeed all the geophysical parameters that are being continuously monitored by the sensor network shows that Arenal Volcano keeps intact its internal energy source, so it remains in its normal condition in an almost regular way.
The present period without lava emission is totally normal and is part of the many "pauses" that historically had taken place before in some of the different manifestations of the activity of this volcano.
Due to this situation it must be taken in accout the serious danger that means the fact of falling in confidence excess about the seeming calm periods of this volcano, and not to make the mistake of trying of climb it and go near the top, because at any time an explosion capable of throwing big sized rocks near the crater (strombolian eruption), can occur, as well as slope down rock avalanches.

Source: El Volcán Arenal no esta inactivo; ni dormido (Arenal Volcano is not inactive, nor dormant). 11 January 2011. Volcanological & Seismological Observatory of Costa Rica. OVSICORI-UNA.


2010 Arenal Volcanic Activity Summary: OVSICORI Report
Normal Activity: Gases Emission, Lava Flows, Strombolian Eruptions and Pyroclastic Flows.
Arenal Volcano have remained a moderate emission of short lava flows, gases and sporadic strombolian eruptions, with small pyroclastic flows originated by the lateral or frontal collapse of lava domes that accumulate at the flanks with high slope.
The collapsing of parts from the top towards the SW, and the detachment of portions of a lava flow emplacement in such direction cause a series of avalanches (pyroclastic flows) that have worried and amazed people in the month of May.
At 24 May happened the reopening of the easternmost vent, which causes the reporting of red-hot material rolling down towards N and E by the northern local residents. People at Z13 (one of the local settlements) witnessed the incandescence from high eruptions full of pyroclasts.
There was no people nor infrastructure affected by avalanches or eruptions.

Source: Resumen de la Actividad Volcánica durante el año 2010 (2010 Volcanic Activity Summary). 20 December 2010. Volcanological & Seismological Observatory of Costa Rica. OVSICORI-UNA.


August - September 2010: OVSICORI Report
Normal Activity: Gas Emission and Strombolian Eruptions.
Arenal Volcano continues its emission of gases and generates sporadic strombolian eruptions. It is reported by the respective villagers the observation of rocks moving towards the N and NE flanks, at the moment of the eruptions.
The crater D (the older) keeps its fumarolic activity. Flanks NE, E and SE remain being affected by the falling of pyroclastic material and acidic rain.

Source: Estado de Los Volcanes. Agosto y Septiembre 2010 (State of Volcanoes, August & September 2010). Volcanological & Seismological Observatory of Costa Rica. OVSICORI-UNA.


24 May 2010: OVSICORI Report
Incandescent flows toward western side of Arenal Volcano.
A series of incandescent flows has been produced at 24 May 2010 in Arenal Volcano. The flows was reported at 10 am, having place the major intensity between 11 am and 1 pm. This activity is normal in Arenal Volcano, which has been active since 1968.

An officer of Arenal Volcano National Park said that several incandescent surges descended by the western hillside. The most distant sections of these flows reached out the tropical forest borderline. A cloud of dust and light materials moved toward north during this volcanic activity. The zone where these detachments happened is located into the managed area of the national park, hence it cannot reach the road, households nor tourism facilities. Geographically the affected sector is the one towards Lake Arenal.

Detachments from the volcano top occurs intermittently as a big mass of recent materials is accumulated and turns down rapidly by gravity. At previous times, with similar features, a lava flow succeeds these detachments. In the next days or weeks, and with clear weather, it can be confirmed this observation. At the very moment that flows was produced, officers of national park closed it, to ensure the tourists safety, and became reopened again at afternoon.

Source: Volcanological & Seismological Observatory of Costa Rica. OVSICORI-UNA. 24 May 2010.


Arenal Volcano Eruption of 24 May 2010 24 May 2010 (10:00 am - 1:00 pm): Pyroclastic Flow Avalanches and Ash
Several avalanches with pyroclastic flows through SW flank and ash fall at N.
At 10 am in the morning of May 24, 2010 Arenal Volcano starts the occurrence of about 10 avalanches with pyroclastic flows up to 1 pm (6 were reported up to midday), with the notoriety that about 8 of them happened in a period of 2 hours (11 am - 1 pm), and there was ash fall over the National Park trails as well over the northern area of volcano region (according to local residents which had to clean the cars). After 1 pm the volcanic activity had continued in a more moderate way.

Authorities from Arenal Volcano National Park have confirmed that the volcanic activity are pyroclastic flows triggered by the detachment of accumulated materials from the active crater area. About 15 pyroclastic flows along the SW flank was observed by local residents and tourist as well; and as effect of this events, a ditch from the top was formed (see volcano gallery above) and is the way for huge and smoky volcanic rocks that roll down near the base of the cone.

The National Park was closed for some hours according to safety guidelines, but as this volcanic activity was confirmed as normal, it was reopened during the afternoon. Experts from RSN at UCR as well as form OVSICORI at UNA will be working on the seismic sensors data in order to update all the information about this volcanic activity.

Source: Arenal Volcano National Park, OVSICORI, RSN; Olger Aragón, Víctor Hugo Quesada and other local residents.


March 2010: Explosive Eruptions with Lava Flow
Small vulcanian eruptions and lava through S flank.
At March 2nd, 2010 (11:30 am) Arenal Volcano has produced one more time an impressive natural spectacle, an eruption of features and magnitude of some unusual amount, according to some eyewitness that were admiring the volcano.
But is merely one event more of its totally normal activity and is no limited to one isolated fact of that day, as inform a researcher from Arenal Volcano National Park which had witnessed the mentioned event. It was a vulcanian eruption of small magnitude, as part of the volcano normal behaviour, which consist in a crater explosion that throws an ash cloud and rocks that fall near the top an roll down along the S flank; this in combination with a red-hot lava avalanche (which can give some red hue to the ash cloud), rise some ash and fine materials; all of this creates a impressive experience.
Arenal activity remains continuous, and currently presents a lava flow along the S flank which in clear nights surely delights the nature admiring public. This volcanic activity, as with the most of the previous events, despite it was covered by some of the main news local agencies, is not an unusual behaviour of Arenal Volcano but a natural spectacle worth of be appreciated within the safety guidelines.
Source: Arenal Volcano National Park.


Arenal Volcano Lava Flow (February 24, 2010) January and February 2010: Lava Flows
Volcanological & Seismological Observatory of Costa Rica Report (OVSICORI).
Arenal Volcano keeps its continuous lava and gas emission and sporadic strombolian eruptions.

About at mid-January a lava flow started towards the S flank. Occasionally some detachments are produced at the crater border or the fore of the flow that originate small avalanches along the SO, S and SE flanks. Some of the blocks reach the vegetation and produce small fires.

Eruption activity remains at low level, due to the quantity of eruptions and the amount of pyroclastic material ejected as well, and there are few eruptions producing ash columns.

Crater D (the old one) shows fumarolic activity. The NE, E and SE flanks remain being affected by the fall of pyroclastic materials and acid rain. Due to the vegetation lost, the strong downhill, the low material consolidation and the high rain fall rates, there are small cold avalanches which are persistent in some of the main streams that emerge there.

Source: E. Fernández, E. Duarte, J. Barquero, W. Sáenz, J.Brenes, M. Martínez, J. Segura, C. Garita. ESTADO DE LOS VOLCANES. Enero del 2010 (OVSICORI).


Arenal Volcano Pyroclastic Flow (July 7, 2009) July 2009: Pyroclastic Flows
Report from Red Sismológica Nacional (RSN).
The Red Sismológica Nacional (UCR - ICE), National Seismological Network, informs (at July 15, 2009) that recent Arenal Volcano activity in the months of June and July corresponds to the natural behavior of the lava flow that remains since beginnings of 2007 through the SW flank, which have produced the pyroclastic avalanches in September 2007 and the ones at June and July 2009 as well. There are also very active fumaroles at the NW side of the crater, that generates some reddish glow in the night.
In 2009, the avalanches happened at June 16 (4 events at 16:34, 16:38, 16:42 and 16:46 p.m), June 23 (15 - 18 avalanches from 11:45 to 13:55, the stronger at 12:02) and July 7 (from 10:30 am). These recent pyroclastic flows are of less volume than the ones from past year; and because to the high declination and the possible change on the lava flow direction, the occurrence of changes in the direction of the future avalanches, is not to be discarded.

Arenal Volcano 3D Seismic DistributionArenal Volcano seismic activity is characterized by showing between 15 and 20 volcano-tectonic seisms per month. Since March 2009, this activity has been increased, generating 67 seisms in March, 32 seisms in April, 45 in May and 21 in June up to the 17th day. After a tridimensional seismic distribution analysis, it is determined that seisms distribute below volcanic structure and its activity is more deeper towards the S and W sectors; which means that these phenomena are related with the volcano own activity and not by faulting.

The seisms below Arenal are observed each time more superficial and its magnitude remain less than the three degrees (Richter scale), thus they are not perceived by local people. It is very likely that this kind of activity suggests that the system had a change in the pressure (either compression or decompression) or it has been a meaningful increasing in the magma feeding, and that the immediate response is reflected in this seismic generation; which matters so much as it has been observed along several decades in this volcano, that precedes the occurrence of pyroclastic flows.
Source: Gerardo Soto & Waldo Taylor. Actividad del volcán Arenal, Junio-Julio del 2009 (RSN July 2009 report).


July 7, 2009 at 10:30 am (16:30 GMT): Pyroclastic Flow
Avalanche by collapse of crater materials and notorious ash cloud.
One more time, consolidating what is now a period of pyroclastic activity, at July 7, 2009 (10:30 am), Arenal Volcano produced an avalanche, along its southern flank, caused by the collapse of accumulated materials from its crater, this time rising an ash cloud of remarkable magnitude. This cloud is formed by particles which are scattered by the wind while are falling down due to its own weight into an "ashes rain". This engaged the administration office of the Arenal Volcano National Park to close it from 10:30 am up to 3:00 pm, not for a possible dangerous condition but the annoyances and confusion that the ash falling may cause in the tourists and visitors, because the normal wind behavior tends to drag it towards the touristic infrastructure of the park. However it was not wind in a considerable way, so almost all the ash collapsed by its weight near the area of the avalanche (southern flank).
All these manifestations in the volcanic activity of Arenal Volcano are completely normal and correspond to its natural behavior according to the geologists which are in continuous monitoring with all the volcanic observatory stations.
Again, it holds the condition that the affected sector does not offer a threat to visitors, park rangers or residents. On the contrary it is located in a safe remote sector of the volcano.
Source: Fabio Arias (Arenal Volcano National Park Manager).


Arenal Volcano (June 28, 2009)June 29, 2009: Moderate Volcanic Activity with Pyroclastic Flows
Arenal Volcano keeps with 2-3 small avalanches per day.
After June 16, 2009 the volcano keeps with a more tone down activity but persistent enough to produce 2 or 3 incandescent avalanches or pyroclastic flows per day. These events are of less magnitude than the ones from the first day. Its origin is due to the collapse of accumulated materials at the crater and its subsequent descend along the volcano flanks, specifically, the southern one. The nature of this phenomenon, a completely normal behavior of Arenal Volcano according to experts geologists, is limited to the external part; that is, not due to internal activity of the magmatic chamber, which remains absolutely normal according to the OSIVAM seismological laboratory constant monitoring.
After all above said, the tourism activity in the zone and into the national park as well, (Arenal Volcano tour) remains normal; allowing the appreciation of the impressive show of Arenal Volcano, while scientists and national park administration keep them in alert and constant vigilance to make this possible.
Source: Arenal Volcano National Park office.


Arenal Volcano Pyroclastic Flow (June 16, 2009)June 16, 2009; between 15:00 and 17:00 local time (21:00-23:00 GMT): Materials Collapse Flow
Avalanche by collapse of crater materials .
Just as one year ago (06/06/2008), at June 16, 2009 between 15:00 and 17:00 horas, OVSICORI received information about an volcanic eruption with reported ash fall in the W sector, where Arenal Volcano National Park is located. At June 17 Eng. Tomás Marino from OVSICORI, visited the volcano to collect data about the reported activity of the previous day at afternoon. It has been confirmed a small eruption, with a very strong sound, which as in previous times triggered an avalanche of materials from the top of volcano. The materials (rocks and less sized particles) has descended towards the SSW volcano flank to reach the altitude line of 800 m above sea level. After this the drag of ashes happened towards the W sector (National Park).
This materials collapse is due to the high slope of the volcano, which favor the fall and transport of materials in a fast way, with the consequent generation of a cloud of ash particles.
In the same way that one year ago, the observatory zone at National Park neighborhood is still safe.
Source: OVSICORI.


October - September 2008: Strombolian Eruptions & Most Recent Picture!
At last! The most recent Arenal Volcano strombolian eruption picture!.
Most Recent Arenal Volcano strombolian eruption picture!It was taken from the room terrace at a local hotel. After several failed attempts to catch a nocturnal Arenal eruption (like the classic pictures from 90's), that privilege was a spontaneous reality in the night of September 09, 2008 at 11:45 pm when Arenal Volcano threw to the air, in a firing spectacular way, some amount of red-hot lava. This happens in the form of volcanic rocks that are thrown by the explosion of compressed gas (as it accumulates due to the internal emission). Because of the high red-hot temperature (more than 700º C), they register (in the camera sensor or film) an elliptic red path according to their parabolic movement while in the air, and erratic lines as rolling down on the volcano flanks.


July 29, 2008: 40th Anniversary of Explosive Eruption of 1968
At July 29, 1968 about 7:30 am Arenal Volcano initiates its current eruptive phase.
After a phase of extraordinary eruptions and lava flows (one of which cross over the current road is dated about 1525) in the conquest period started by Columbus in Costa Rica, Arenal Volcano has gone over an inactive stage, such that in the first half of 20th century it has been called "Arenal Peak ". This peculiar peak of almost perfect conic shaped, warned with thundering and local trembling to inhabitants of two small villages near its base at northwest. In the morning of July 29 happened a furious volcanic eruption with a big explosion that released abruptly the amount of accumulated energy, precisely at the base of the cone al northwest and toward the villages, exterminating the people that was in home (mainly women and kids) by the cataclysmic bombing of huge rocks and burning avalanches (pyroclastic flows). In such explosion, it has been opened three vents; one of them near the top, which by the accumulation of continuously poured materials has shaped the main cone with the current active crater, that surpassed the former cone and even more started to fill the old inactive crater.


July 2008: Strombolian Eruptions
Arenal Volcano delivers again its classic fireworks show.
Archived picture (from 90's) of a strombolian eruption.In several days of July it has been reported volcanic eruptions of the strombolian type (lava is thrown up to the air by explosion), which apparently has not been photographed since more than 10 years ago (The illustrative picture is from 90's). Indeed, the author has been able to see one of them, from the terrace at a local hotel, in the night of July 23, 2008, at 10:15 pm; unfortunately without the camera ready. With a powerful thundering, red-hot rocks raised from the crater and fell down near top of volcano and rolled down by the flanks like fire avalanches, all after about 10 seconds of air flight!

 


Arenal Volcano Pyroclastic Flow 2008-06-10June 10, 2008 at 7-8 am (13-14 GMT): Pyroclastic Flow
Incandescent avalanche recurs (See Arenal Volcano Gallery for pics).
This event occurred again towards SW Arenal Volcano flank, indeed it was throughout the gutter caused in the flow of the past June 6. Again a cloud of thin ash has moved depositing material towards W and NW along an horizontal distance of 4 Km; because of which a partial closing of National Park area was done. An activity of explosive eruption is discarded as a source for concern. Despite the fact that next to the cloud of materials a tall column of gas and steam was generated, this fact did not represent a direct threat to aviation. Even more the fall of solid materials is produced in a few tens of minutes and with light rain conditions, in less time. The unstable material (from summit to rest area) will keep descending. Fragments of big size, generated from the top or along the gutter can repeat this at anytime. The facilities and observatory zone at National Park neighborhood are still safe.
Source: OVSICORI.

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Arenal Volcano Pyroclastic Flow 2008-06-08June 6, 2008 at 9:15 am (15:15 GMT): Pyroclastic Flow
Incandescent avalanche triggered by lava flow collapse.
A hot avalanche rolled down the SW slopes of Arenal Volcano. An unestimated amount of blocky, andesitic lava that was accumulating, on the summit of Arenal Volcano, since March 2007, collapsed due to the extrusion of a lava flow. Even though fragments of such lava flow fell intermittently over these 14 months, it was until now that a mayor avalanche took place. The present collapse provoked a scar of some 800 m long from the summit to the bottom. Lose, dry, incandescent material was canalized down the slope conforming a wide chaotic "fan" *, at approx. 900 m asl. Dust and fine ashes deposited in a small area W and NW of the active flank of volcano. Rain rapidly diluted the fine film that was deposited on vegetation.
The affected sector does not offer a threat to visitors, park rangers or residents. On the contrary it is located in a safe remote sector of the volcano.
Source: OVSICORI.
* a fan-shaped talus deposit (sloping mass of rocks and fragments) at the foot of the slope.

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Arenal Volcano & Volcanism Related Books

This is a selection of recommended and suggested books for further reading and learning about geology, volcanoes or volcanism phenomenon; which are available for look at their reader reviews and buying online if needed.

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Notes & References:
(Repeated citations ordered in parenthesis)
1
(1, 2, 3) - Soto, G.J., & Alvarado, G.E. (2006). Eruptive history of Arenal Volcano, Costa Rica, 7 ka to present. Journal of Volcanology and Geothermal Research, 157(1-3), 254-269.
2
(1, 2) Molina González, Jorge Rolando. (2003). El Volcán Arenal: El Coloso de San Carlos. Personal edition. San José, Costa Rica.
3
Soto, G.J.; Alvarado, G.E.;Bolge, L.L.; Schmincke, H. & Sumita, M. (2006). The 1968 andesitic lateral blast eruption at Arenal Volcano, Costa Rica. Journal of Volcanology and Geothermal Research, 157(1-3), 9-33.
4
As measured in 2007. Geodetic Deformation Monitoring. Volcanological & Seismological Observatory of Costa Rica. OVSICORI-UNA.
5
Gerardo J. Soto (February 2011). Geologist (ICE/Universidad de Costa Rica). Personal communication.
6
Duarte, E. (2010). Las Plumas de Gas y Vapor en Volcanes de Costa Rica. Observatorio Vulcanológico y Sismológico de Costa Rica. OVSICORI-UNA.
7
Duarte, E. & Fernández, E. (2010). Los Domos Volcánicos y Sus Características. Observatorio Vulcanológico y Sismológico de Costa Rica. OVSICORI-UNA.
8
Soto, G.J.; Alvarado, G.E. & Sjöbohm, L. (2007). Volcano-Geology and Stratigraphy as Basis for the Mapping of Volcanic Hazards at Arenal, Costa Rica. 20th Colloquium on Latin American Earth Sciences. Kiel, Germany.
9
Alvarado Induni, Guillermo. (2008). Los Volcanes de Costa Rica: Geología, historia y riqueza natural. UNED. San José, Costa Rica.
10
Barquero, Jorge. (1999). Volcán Arenal. Bilingual personal edition. San José, Costa Rica.
11
The camera does not deliver image during night. Besides, the webcam technology is subject to the hard weather conditions (and even to the wildlife!), because of which it requires such maintenance, that some interruptions and out-of-service periods are not avoidable, but it returns to the normal work as soon as possible according to the possibilities.
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