As so often, and generally without intention, I have hit upon yet another volcano that has all the trimmings of a beast but seems not really to be recognised as such. Up to a few years ago there have been very few studies to find out about the seismological and structural properties of the volcano. Volcán Ceboruco is considered among the five volcanoes with the highest risk in Mexico, and the second most active after Colima volcano in the western Trans-Mexican Volcanic Belt. Yet, scientists had to point out, in a 2016 study, “that every effort should be made to monitor its seismic activity”.
Volcán Ceboruco is located in central western Mexico, one of the geo-tectonically most complex regions of the country. Here the convergence and continual interactions of several geological structures are responsible for a lot of seismicity, often felt by the residents in earthquake swarms or individual larger events. The main actors are the subducting Rivera and Cocos plates who dive under the North America Plate. This subduction has created the Trans-Mexican Volcanic Belt (TMVB, Spanish: Sierra Volcánica Transversal) – a continental arc some 1000 km long – extending from the western coast across the country to the Gulf of Mexico in the east. This belt divides the Sierra Madre Occidentale in the north from the Jalisko Block to the south of it.
Ceboruco sits in a large depression in the westernmost part of the highly fractured TMVB. This Ceboruco (half-) Graben is part of the Tepic-Zacoalco Rift (or Graben), which has a NW-SE orientation and forms a triple junction near Guadalajara together with the N-S oriented Colima Rift and the E-W Chapala Rift. The Tepic-Zacoalco Rift is also the northern border of the Jalisco crustal Block which is rifting away from the North American plate in SW direction. This breaking off is probably related to opening of the Gulf of California. So, volcanism in these parts is driven not alone by subduction along the Pacific coast but also by rifting and stretching of the crust.
Note: Gardner et al. had published a paper in 2000: “The caldera-forming eruption of Volcán Ceboruco”. Also, in other research papers (as well as in GVP descriptions) the term summit ‘calderas’ is used. However, I noticed that in some more recent papers the authors took care to use ‘craters’ instead throughout. I’ll stick with the respective sources’ terms here.
Volcán Ceboruco is an andesitic and dacitic stratovolcano north-west of the towns of Jala and Ahuacatlan in the federal state of Nayarit. Its name in the Nahuatl language was originally ‘Tonan’. There are quite a few Pleistocene volcanoes at this end of the TMVB, but Ceboruco is the only one with confirmed historical eruptions. There have been at least eight from this volcano in the last one thousand years, bringing the average to one eruption every 125 years. The events confirmed by historical observations were those chronicled in (1542-? 1567-?) and in 1870-75, the last with a VEI of 3 and well documented by eyewitnesses.
Of Craters and Lava Flows
Ceboruco’s eruptions are mainly effusive; however, studies of the eruptions reveal a great variability of eruptive styles throughout its record of activity. Rows of monogenetic edifices have erupted along a NW-SE-trending line cutting across Ceboruco. There are 18 scoria cones (and their lava flows), 8 silicic lava domes, and 2 phreatomagmatic pyroclastic cones. Recent monogenetic activity along the Ceboruco graben extends to an area SE of Ixtlán del Río, six basaltic-andesite scoria cones occur here aligned in a NW–SE direction.
The volcano is 2265 m high and features two concentric summit calderas. The VEI 6 eruption of the voluminous rhyodacitic Jala Pumice, one of the largest known in México during the Holocene, formed the initial, 4 km wide caldera about 1000 years ago.
After this devastating event at least seven major lava flows and several lava domes were emplaced. On first sight some of the flows appear very youthful and have remained unvegetated. However, newer dating suggests that all lava flows from Ceboruco – except the 1870 flow – were emplaced within ≤140 years after 1005 AD. If this is correct, the volcano had a nap of ~800 years before it sent down its latest lava flow. This long pause would serve to explain the production of dacite lavas next to basaltic andesites: in a shallow reservoir magma differentiation could have taken place and then erupted the more evolved lavas together with primitive material from a new batch.
An inner crater was formed by the drainage of the voluminous Copales lava flow and subsequent collapse of the large dacitic Dos Equis lava dome. Actually, the walls of the inner crater are all that is left of Dos Equis. Today several volcanic structures can be seen on the inner crater floor. There are lava domes, pyroclastic and ash cones with their associated lava flows and scoria deposits. Some active fumaroles remind of the ongoing activity in the volcano.
The crater walls of Ceboruco are breached to the N and SW facilitating the frequent emplacement of pyroclastic deposits and lava flows along barrancas in these directions.
The first rifting-related volcanic evidence were a number of lava flows dated at 8 Ma which immediately overlie rocks of the Jalisco Block to the S. The activity of the more modern Ceboruco graben probably started in the early Pliocene, because the older Jala ignimbrites and rhyolites (4.8 to 4.2 Ma) are cut by the fault which marks the NE boundary of the graben. Younger deposits though, dated at 3.8 Ma, cover this same fault unbroken.
In the past 100 ka Volcán Ceboruco produced some 51 km³ of volcanic materials, an equivalent to an eruption rate of ∼377 m³ per square kilometer per year. At least one other stage of cone-building happened before the present Ceboruco volcano was constructed. During this oldest stage the principal edifice was built from successive thin aa-type andesitic lava flows and breccias. Nothing has been found of activity in the last 45 ka up to 1000 years ago; it is thought that the volcano was quiescent during that time.The next dated event, after the long pause, was the so-called Jala Plinian eruption.
The Jala Plinian eruption
After a ~44 ka (!) dormant phase, Ceboruco volcano erupted violently (VEI 6) around the year 1005, expelling 3-4 km³ of magma during the Jala Plinian eruption. Researchers calculated that the Plinian column was of 25-30 km in height. The widely distributed deposits are known as the Jala Pumice.
Shortly before this eruption, a compositional change from the uniformly andesitic lava flows to more evolved magmas had taken place when the trachy-dacitic Destiladero lava flow was emplaced on Ceboruco’s NW flank. The following catastrophic eruption included major changes in eruptive style and magma composition, compared to the first cone-construction phase. Pumice fall-out was deposited mainly to the NE and associated pyroclastic flow and surge deposits were mainly emplaced to the SW. The majority of pyroclastic flow deposits produced during the Jala eruption was emplaced to the SW on the Marquesado ash fan, where they reach a total thickness of up to 60 m. White (rhyodacite) and gray (dacite) pumices occur in every tephra layer. The products of this eruption plus subsequent lava flows constitute ∼13 km³ of the total volume of Volcán Ceboruco.
Pottery fragments found directly underneath the Jala pumice deposit indicate that the area around Ceboruco was inhabited by human populations who witnessed this eruption. The age therefore represents an important time marker in the prehistory of this region, because an area of >560 km² was devastated and covered by an average thickness of >50 cm of pumice and ash.
Seeing the size of this eruption it does not surprise that in 2018 tephra particles from it have been identified for the first time in Europe. Ash samples from western Ireland, that could not be assigned a source previously, have now been found to originate from the great Jala Plinian eruption of Ceboruco.
The braided, andesitic El Norte lava flows cover most of the northern flank of Ceboruco volcano. These were erupted along ring fractures along the crater/caldera rim and blanket a 3.5 km length of the northern flank. Their youthful morphology and unvegetated surfaces suggested an apparently very young age, but probably date back to very shortly after the Plinian Jala eruption. The El Norte flow also covers the vents of three older lavas: The andesitic Cajón lava flow (which itself is overlain by the trachy-andesitic Coapan 2 lava flow) and the Coapan 1 lava flow of basaltic trachy-andesite composition.
The almost 9 km long, very fresh-looking unvegetated El Ceboruco flow on the volcano’s SW flank has long been thought to be very young, no more than a couple hundred years old. But no, it is the second youngest and, like the others here, was erupted almost a thousand years ago. Today it is crossed by the Mexican Federal Highway 15 and a railway line.
The screenshot below is from the most beautiful photo sphere I have seen for a long time; check it out on GMaps HERE .
Two more eruptions are mentioned in 1542 and 1567, but obviously they did not produce lava flows. No convincing evidence has been found yet that these have taken place at all.
The 1870-75 Eruption
Ceboruco’s single well-documented historic eruption started in February 1870 and lasted at least until 1875, when still small ash-laden eruptive columns were rising at intervals of 10 min. For more than a decade Ceboruco was a topic in local newspapers. Also, the local government had sent committees of engineers and local people to the volcano several times to investigate the situation. These archived contemporary reports and illustrations are a valuable help in reconstructing the events.
There have been signs of reactivation long before the volcano actually awakened – as early as 1783. Reports from 1832 mention subterranean noise and seismic activity. These were felt strong enough to frighten the inhabitants of Jala and to leave their homes for a few days. Direct precursors of the eruption included noise, seismic activity, and white vapor emanating from the summit area.
The eruption began with an explosion and emission of vapor and ash, then a fire-column”. On February 23, columns of steam and ash, strong noise and small earthquakes were reported. At night people noticed “fire” coming out of the crater at 4 or 5 different locations. Also, at the beginning of the major eruptive phase “boiling sand, moving like water” flowed down the Los Cuates barranca. By the end of February, “various” ash columns were noted along fractures in the Los Cuates barranca, from which lava was emanating. Later descriptions go from noise similar to “ocean waves during a storm” to “whistles like a locomotive”, thick columns of black “vapor” was seen and “fire” in the crater during night. By June that year Ceboruco is active without cessation, ash falls with such density that people in Marquesado village (S of Ceboruco) can hardly see.
Most obvious evidence of this eruption is the 7.5 km long dacitic lava flow which was emitted from the summit crater and flowed down the W slope of the volcano. It was described as slow-moving, very viscous, and its front was 80 m high. The lava flow advanced along Los Cuates barranca for little more than two years until it stopped moving in 1872.
This 5-year-long eruption had very unpleasant impacts on the surrounding villages and their residents. Skin and breathing-tract diseases affecting people in nearby villages were reported. Also, cattle and wild animals suffered mortal teeth abrasion from chewing plants powdered by fine ash.
Decades after the eruption, when geologists studied the written accounts of the time, they recognised that “nuée ardentes” were described here, in a way very similar to that in reports of Mt. Pelée’s eruption of 1902.
19 years after the eruption two major fumaroles were still active within the 1870 crater area with temperatures of 96°C. Additional fumaroles were visible along the 1870–72 lava flow. To the present day Ceboruco has remained in a fumarolic stage. Even though the activity has diminished somewhat over time, fumaroles at the summit had still temperatures between 84°C (outer crater) and 92°C (inner crater) in 1994.
ANY RISKS? YES – SOME!
As with all active volcanoes in densely populated areas Ceboruco does pose a risk that must be addressed by the authorities. Numerous towns and villages are dotted in the area, additionally there are two national roads and a railroad line. Populations of more than 55,000 live within 10 km and 1,282,014 within 100 km. The town of Jala alone, beginning 5 km from the crater rim, had over 9600 residents in 2005, fifteen years ago. Lahars could also seriously affect the operation of existing El Cajón and La Yesca hydroelectric power plants, wet ash falling on electric lines could cause serious transmission problems, power outages etc.
From several studies it becomes clear that future eruptions should not only be expected from Ceboruco’s crater area, but to a minor extent also from adjacent areas to the NW and SE. At least 11 monogenetic eruptions have occurred during the Holocene along a 2 km wide and ca. 30 km long stripe that intersects Ceboruco’s crater in a NW–SE direction.
Lately there have been pressure increases reported in the volcano. Sánchez et al. studied the seismicity at the Ceboruco Volcano during the period 2003 to 2008. They found that there are low-frequency events due to changes in the pressure of subsurface fluids. Together with the time from the latest eruptive activity, which is longer than the estimated recurrence time, these indicate that Ceboruco volcano should be considered of high hazard, and that every effort should be made to monitor its seismic activity. Actually, every paper I’ve seen (except one that was aimed at geothermal exploration) has given this same advice at the end.
I don’t know how far measurements have been implemented after all these studies. I have found nothing on “monitoring Ceboruco” on the Cenapred website or anywhere else. But then, I cannot search in Spanish. Anyway, it seems that a large study project is/has been carried out which involves a dense temporal seismic network of 25 stations covering an area of 256 km²: “Local Seismicity in the Ceboruco Volcano Region, Mexico”. Moreover, a large team of scientists (e.g. K. Sieron, et al.) are working on a detailed hazard map for the volcano’s surroundings, taking in account all possible eruption scenarios. So, hopefully we will soon learn more about the present state of the volcano on the one hand, and see more protective measures coming in place on the other.
Disclaimer: I am not a scientist, all information in this (and any of my other posts) is gleaned from the scientific www and/or from books I have read, so hopefully from people who do get things right! 🙂 If you find something not quite right, or if you can add some more interesting stuff, please leave a comment.
Enjoy! – GRANYIA
SOURCES & FURTHER READING
– GVP, Ceboruco
– Local seismicity in the Ceboruco Region (2018, Poster)
– Insights about the activity of the Ceboruco Volcano (2013)
– Subsurface structural imaging of Ceboruco (2019, paywalled)
– The caldera-forming eruption of Volcán Ceboruco, Mexico (2000, paywalled)
– Palaeomagnetic dating of two recent lava flows from Ceboruco (2016)
– Geology and Petrology of Volcan Ceboruco (1980, paywalled)
– …stratigraphy and eruption rates of Ceboruco… (2008)
– Constraints on Jalisco Block Motion and Tectonics of… (2011, paywalled)
– Magma eruption rates … Ceboruco–San Pedro volcanic field (2004)
– Seismicity at Ceboruco Volcano (2009)
– Volcanic Travels Blog – Stories of fieldwork and life as a volcanologist