Breached caldera and active cone at Galeras looking to the south. Image courtesy LeChaudron de Vulcain, Oct 2019
Galeras is a stratovolcano in the SW corner of Columbia. It is one of Columbia’s most active volcanoes. The active cone is over a million years old. The volcano is 9 km from Pasto (San Juan de Pasto), a city of over 500,000.
The volcano tops out at 4,276 m and was designated part of the Decade Volcano Program by the UN in 1991 due to its violent eruptive history and proximity to large numbers of people.
Pasto is a regional capital and sits at an altitude of 2,897 m. It was founded by Spanish conquistadors in 1537 and has become the administrative, cultural and religious center of the region since colonial times.
Volcano hazard map of Galeras superimposed on Landsat imagery of surrounding communities. Red is highest risk, generally pyroclastic flow. Yellow is significant tephra fall. Image courtesy H. Villegas, 2002
Climate is warm-summer Mediterranean with relatively consistent temperatures throughout the year. It averages around 800 mm of rain per year.
Economy in the town is primarily trade and service. Rural areas around the city are faming, cattle ranching and a small-scale mining industry.
INGEOMINAS monitors volcanos in Columbia.
Volcano Discovery has links to Galeras webcams. I saw no images displayed.
Windy.com also has a webcam at Villa Angela in Pasto pointed at Galeras that is active.
Tragedy
Galeras erupted with no warning Jan 14, 1993 while a group of volcanologists and visitors were in the crater. Nine were killed and six injured in the explosion. Those in the crater did not have adequate safety gear mostly due to the lack of seismic activity before the eruption. One of the positive outcomes from the eruption was new emphasis on proper clothing and equipment when visiting volcanoes.
There was a Decade Volcano conference in Pasto in 1993. Several scientists present did an impromptu visit to the volcano on Jan 14. The eruption took place unexpectedly while they were on the summit.
Geoffrey Brown and Fernando Cuenca in preparation for field research on Galeras Jan 1993. They did not return after the eruption. Other two gentlemen are unidentified. Image courtesy Wiki, Jan 1993
Finger pointing and blame placing quickly took place with media claims that the expedition leaders were reckless and ignored a prediction made three days earlier by recorded seismic activity. This particular type of activity had been seen and tentatively used to predict eruptions on some andesitic volcanoes before this eruption. It only showed up on signals recorded from a single seismometer. Based on previous history of Galeras, it was the opinion of the scientists this was not yet predictive of any future volcanic activity from the mountain at the time.
The Jan 14 explosion was preceded by a period of generally declining activity following destruction of an extruded dome July 1992. Starting Jan 1, a distinct seismic event started appearing, the tornillo. Tornillos are a special type of long period event, with nearly perfect symmetry and an extended tail. They are thought to represent fluid resonance in a cavity. 2 were recorded in Mar 1989, 9 events in 5 days before the dome was destroyed in July, and a single event on Aug 3 not followed by an eruption. The January events were not identical to the each other or earlier events.
Long-period events at Galeras in the period from reactivation to its Jan 1993 deadly eruption. Note how the volcano really quieted down after destruction of the dacite dome July 1992. Image courtesy Smithsonian GVP, Dec 1992 Bulletin Report
The eruption had no immediate precursors in the hours before it. The seismic signal of the eruption lasted 15 minutes. It produced a plume up to 4 km above the vent.
Two volcanologists were taking gas samples inside the active crater at the time of the eruption. 4 others were taking gravity measurements along the W side of the active crater rim minutes before the eruption. A third group of 4 volcanologists and three tourists were on the SE flank of the active cone.
The eruption was a vertical Vulcanian eruption immediately producing a lot of very large ballistics. There were tongues of convecting plumes 5-15 m across the flanks of the cone, though no pyroclastic flows were produced. Tephra was quite large and hot, with individual chunks as much as 1.5 m across. None of the volcanologists or tourists wore hard hats. Fall of large tephra stopped after a few minutes. Vigorous degassing with a loud jet noise continued for hours after the explosion. There were no subsequent explosions.
Sketch map of active crater of Galeras and locations of people injured and killed during Jan 14 eruption. Image courtesy Smithsonian GVP, Dec 1992 Bulletin Report
Some of the injured were able to move downslope and start climbing the outer crater wall where they were rescued.
Seismicity after the eruption reached the highest levels yet recorded at Galeras with 611 long period events recorded within the first 12 hours after and another 150 recorded the following day. Some of these were individual pulses of gas relief. An additional small ash emission and volcanic tremor took place on Jan 15.
The eruption produced some juvenile material, some altered material, and some material from the dome destroyed July 1992.
Memorial sign to the eruption and lost of life on Galeras, Pasto, Columbia. Image courtesy Wiki, Apr 2018
One description of the buildup to the eruption suggests that gas pressure had been building beneath Galeras since the dome was destroyed in July. Gas was trapped in the pore spaces of relatively impermeable rock. After a certain point, the rock ruptured and the eruption took place. There is also a possibility that it was initiated phreatically.
Two books came out of this, one by surviving volcanologist Stanley Williams in 2001 entitled Surviving Galeras. The second one was by Victoria Bruce in 2001 entitled No Apparent Danger: The True Story of Volcanic Disaster at Galeras and Nevado del Ruiz. Williams describes the event from his perspective as a survivor. Bruce is much harsher, describing professional and governmental failures that led to the deaths on Galeras and lahars from Nevada del Ruiz that killed 23,000. Both are useful to read to glean the entire story of what happened and why.
Landsat 5 Thematic Mapper image of Galeras (center with active fumaroles) and Pasto (immediately to the right). Amphitheater from flank collapse pointing to the west along with debris downslope. Image courtesy NASA Earth Observatory, Aug 1989
Volcano
Galeras is an andesitic stratovolcano. The current active cone fills an amphitheater formed by a flank collapse and subsequent debris avalanche. The current cone is around 5,000 years old. Dating of the currently active cone identified six major periods of eruptive activity along with 45 individual pyroclastic flows, tephra falls, lava flows and lahars. The most common historic events from the current Galeras cone are pyroclastic flows. Current hazard maps of Galeras define zones of high hazard as those with pyroclastic flows, those of low hazard as those with tephra falls and secondary lahars.
Recent eruptions from Galeras have been Vulcanian, with occasional pyroclastic flows, degassing with significant SO2 and ash plumes.
Debris avalanches are a major concern at Galeras. The volcano has an extensive hydrothermal system which has altered rocks that the cone is constructed of, weakening it, and making future collapses more likely. There are at least three known flank collapses from Galeras.
Gas and steam emissions from crater at the summit of Galeras Apr 2013. Image taken from caldera rim at the summit, courtesy SGC, Apr 2013 via Smithsonian GVP Bulletin Report Jan 2018
The ancestral Galeras volcanic complex was built in at least four stages. The two oldest stages, Cariaco and Pamba are the westernmost activity of the complex. The Coba Negra edifice was partly destroyed by a caldera forming eruption 560,000 years ago. It had a total volume of around 70 km3. The eruption produced some 16 km3 of pyroclastic flow deposits. The caldera destroyed in the eruption was 5 km in diameter. The next construction phase is called the Jenoy, and mostly rebuilt the edifice with a final volume around 64 km3. The caldera-forming eruption took place 150 – 40,000 ago. There were only about 2 km3 of deposits from these eruptions, mostly on the NW and SE slopes of the complex. The center of the Jenoy caldera was ESE from the previous Coba Negra caldera. It was some 4 km. There was a summit collapse, not thought to be eruption related 12 – 5,000 years ago during the Urcunina stage. Hydrothermally altered rocks are found in the scar of the collapse that suggest it was due to instabilities created by the hydrothermal system of the volcano. There are around 4 km3 of structure missing from the volcano, with around 3 km3 of avalanche deposits found near Consaca 12 km west of the current summit. In the past, this system has produced large, explosive eruptions, though most of them in recent years have been smaller.
Summit crater of Galeras Aug 2016. Several points of gas emissions from active fumarole craters within and surrounding the summit crater. Image courtesy SGC via Smithsonian GVP Bulletin Report Jan 2018
Two zones of strong scattering have been identified below the volcano. The shallow one is 4 – 8 km and the deeper one is imaged below 13.2 km, as much as 37 km below the volcano. Magma appears to be degassing at depth beneath the volcano. This degassing reduces volcanic gasses in the magma and in turn pressurizes the system which then causes explosive eruptions. At the same time, the shallow hydrothermal system weakens the surrounding rock, also making explosive eruptions more likely.
Tornillo event recorded at Galeras Nov 14, 2011. Image courtesy INGEOMINAS via Smithsonian GVP Apr 2012 Report
Tornillo
Tornillos (Spanish for screw) are a pre-eruption seismicity. They were first recognized at Redoubt and Nevado del Ruiz. They are long-duration seismic events, with a sharp frequency peak and a long tail (coda). They are thought to be generated by fluids filling a cavity, shattering of rock due to increased fluid pressure as magma moves through the crust. They are generally shallow, less than 1.5 km below the surface.
Observations of these at Galeras were the first detailed study of these sorts of signals, though they have been seen in multiple other locations. At Galeras, they correlative closely with ash eruptions and are used for potential eruption forecasting. Study at Galeras has identified 13 types of tornillos.
Predictions of Galeras eruptions have improved over time, as tornillos now correlate with about 80% of eruptions. The number of these recorded before eruptions also seems to correlate with the size of the impending eruption.
Steam plume from Galeras Apr 2012. Photo taken from Pasto, courtesy SGC via Smithsonian GVP Jan 2018 Bulletin Report
Eruptions
Historical records of Galeras eruptions date back to 1535, with periods of activity taking place every few decades. Recent eruptions have been more frequent and included dome construction, explosions, and persistent seismic activity.
The oldest activity has been dated around 7050 BC. Other eruptions like this event took place 2580 BC, 1160 BC, 490 BC, and 890 AD. The Smithsonian GVP lists 2 VEI 3 eruptions in the 16th Century, three more in the 17th Century, 5 VEI 2 – 3 in the 19th, and at least 10 VEI 2 in the 20th with the last one in 1974. Smaller eruptions before the 20th century are likely not listed.
It is not uncommon for the volcano to go relatively quiet for 2 – 3 decades between periods of activity. The most recent of these was 1974 – 1988.
Ash emission from Galeras May 2012. Image from NW flank, courtesy SGC via Smithsonian GVP Bulletin Report Jan 2018
Smithsonian GVP lists bulletin reports for activity from Galeras since its reactivation Feb 1989. The earliest reports unpublished data that people living near the volcano reported brief activity each year 1974 – 1983. Soldiers manning a communications facility on the caldera rim reported increased gas emissions, seismicity and increased rockfall activity early in 1988, a year before the GVP bulletin reports began. If nothing else, this demonstrates that both the locals and the national government were comfortable with having people on the volcano.
Fumarolic activity with minor ash emissions and seismicity increased Feb 1989. There was a minor explosion Feb 19 followed by a short water, SO2 plume a couple hundred meters high above the crater. One of the craters became active with ash 1 km from the vent. Ash emissions waxed and waned through March with a strong ash emission on Mar 27. Activity continued to ramp up through April with frequent ash emissions and increased seismicity. By early May, plume heights reached over 3 km and dusted over 33 km2 near the volcano and neighboring towns. Activity waxed and waned for the rest of the year and through 1990.
Ash emissions from Galeras Dec 2013. Image courtesy INGEOMMINAS via Volcano Discovery, Dec 2013
Frequent ash emissions, incandescence and more frequent earthquakes continued in the first half of 1991, increasing by Sept with tephra emissions and a lava dome in the summit crater in Oct. Peak activity decreased in late Oct before resuming in April 1992. The dome was destroyed in the largest explosion since 1989 on Jul 16. Activity declined by the end of July through Dec.
This all led to the deadly Jan 14, 1993 eruption.
Periodic activity continued following the Jan 14 eruption, with the largest being one of Mar 23 and June 7. Both produced pyroclastics, columns 7-8 km, and dusted areas as far as 100 km from the volcano. 42 tornillos were recorded in Mar. 104 were recorded Apr 18 – Jun 7. The Jun 7 eruption was the fifth one of 1993. Activity declined following the June 7 eruption.
Active crater of Galeras from above. Undated photo courtesy The Watchers Blog, Nov 2011
The period after Jun 7, 1993 – Mar 2000 was marked by low level seismic events, tornillos, continued fumarole and gas emissions. Eruptions resumed Apr 22 and May 18, 2000 with two small eruptions, both preceded by tornillo events. Earthquakes continued following the May eruption with continuing fumarole and gas emissions from the crater.
A new eruptive episode began June 2004. This included gas and ash emissions in July. An eruption on Aug 11 sent a plume SW into Ecuador. Satellite imagery shows the plume rose almost 11 km. The volcano erupted explosively again Nov 21 producing a 9 km plume.
Activity forced the Columbian government to evacuate around 9,000 near the volcano due to shallow earthquake activity in May 2005. Occasional steam plumes were visible from Pasto. Periodic increases in activity, eruptions, ash clouds, pyroclastic flows, over the last 15 years have been observed. The most recent of these was 2014.
General tectonics of Carnegie Ridge subducting under southern Columbia / northern Ecuador. Image courtesy mikenorton via Wiki, Aug 2010
Tectonics
The general tectonics of the Northern Andes in Columbia is driven by the subduction of the Nazca Plate under the South American Plate. In Columbia, this subduction is complex, involving a block, the subducting Carnegie Ridge, all taking place at the very northern portion of the Nazca Plate. The boundary between the Nazca Plate and the Cocos Plate to the north is a series of spreading centers, called the Malpelo Rift.
Subduction rate by the Nazca Plate beneath South America is 5 – 7 cm/year. Spreading rate between the Cocos and Nazca Plates is 6 – 7 cm/yr. Plate motion under this portion of Columbia has almost an ‘S’-shaped form, with an initial offshore dip to a depth of around 100 – 120 km after which the subduction flattens out to nearly a flat-plate subduction underneath South America. There is nearly a complete absence of intermediate depth seismicity (below 90 km).
Detailed schematic of tectonics of northern Andes. Image courtesy Gutscher et al via Earthjay.com, Feb 2019
A 1999 paper by Gutscher et al makes the case that the various regions of volcanic activity in the Northern Andes (Columbia and Ecuador) are due to a dual tear in the subducting Nazca Plate. The center portion of the subducting Carnegie Ridge is generally flat plate subduction under South America. On either side, there are tears. Seismic gaps are relatively common where an oceanic plateau or other structural high (seamount chain, spreading center) collides with the trench. The active volcanic arc is broad and chemically anomalous. One of the arguments against this continuation of volcanic activity where there should be a ridge-induced volcanic gap. This is based on a model that subduction of this ridge began only 1 Ma rather than 8 Ma. The buoyant portion of the Ridge continues as far as 500 km eastward from the trench. Finally, the ridge must be thicker than 17 km to resist subduction, which it is.
Dual tear subduction model for subduction of Carnegie Ridge under northern Andes. Image courtesy Gutscher et al via Earthjay.com, Feb 2019
Subduction of the Carnegie Ridge is taking place underneath Galeras and to its south. Subduction of the spreading centers takes place to the north of Galeras. In volcanic terms this ends up segmenting volcanic activity in Columbia. The Carnegie Ridge has been subducting for at least the last 2 Ma and more likely the last 8 Ma.
The 1,100 km from 5 N to 3.5 S is a discontinuous band of stratovolcanoes and rhyolitic ash sheets. The arc is one of the least studied in the world. The northern portion is a single 90 km row of stratovolcanoes, Ruiz to Machin. The southern row has 9 volcanic centers and a young cinder cone field. The youngest magmas in this portion are all andesites. From Galeras southward into Ecuador, volcanism becomes more abundant, variable and widespread. There are four rows of volcanoes extending along this part of the arc. The western row is a continuous front 270 km long with regularly spaced stratovolcanoes. All of these are breached calderas surrounded with widespread pyroclastic deposits.
Steam plumes from active fumaroles on active cone in Galeras, Apr 2015. Image courtesy SGC via Smithsonian GVP Jan 2018 Bulletin Report
Conclusions
Climbing and sampling active volcanoes is a dangerous business. The good news is that there are lots of dangerous businesses. The bad news is this is one of them. People were killed in this one, and the survivors were changed for life. Traumatic brain injury, broken limbs and multiple surgeries afterwards will do that to you. Still, the overall community did learn something out of this one. For this volcano, they learned to pay very close attention to tornillos. They also learned to get serious about a kit for visiting volcanoes, hard hats and some sort of heat-resistant clothing being near absolute requirements. Military aviators, oilfield people, and many other professions work in these because they work. As the years go by, that kit will improve. It appears it already did, at least in some measure at White island, Dec 9, 2019. Prayers for the departed and survivors, as they are on a long, frustrating, painful, difficult journey.
Galeras from Pasto in the evening. View is looking to the north. Image courtesy Jorgelrm via Wiki, Dec 2005
Additional information
https://geology.com/volcanoes/galeras/
http://volcano.oregonstate.edu/oldroot/volcanoes/galeras/galeras.html
https://earthobservatory.nasa.gov/images/5561/galeras-volcano-colombia
https://earthobservatory.nasa.gov/images/81223/sizing-up-galeras
https://link.springer.com/referenceworkentry/10.1007%2F978-1-4020-4399-4_349
http://www.januarymagazine.com/features/surgaleras.html
https://volcano.si.edu/volcano.cfm?vn=351080
http://www.scielo.org.co/scielo.php?script=sci_arttext&pid=S0120-02832012000200008
https://www.latimes.com/archives/la-xpm-1993-01-25-mn-1676-story.html
https://www.sciencedirect.com/science/article/abs/pii/S0377027396001035
https://www.science.gov/topicpages/g/galeras+volcano+colombia
http://geomorphology.sese.asu.edu/Papers/gregory-wodzicki_andes_uplift_gsab00.pdf
https://www.sciencedirect.com/science/article/abs/pii/S0377027396000832
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