In our modern world, no animal has gone extinct because of a volcanic eruption – as far as we know! That should not come as a big surprise. Volcanoes tend to affect fairly small areas around them, at least regions that are much smaller than the typical areas where species live. One animal particularly at risk would be the giant tortoise of the Galapagos. If you are a tortoise, outrunning a pyroclastic flow (or even an effusive lava flow) does present a challenge. But the frequent eruptions affect only part of the islands, and enough tortoises happen to be visiting somewhere else at the moment when a Galapagos volcano erupts, following Geolurking’s advice on catastrophes (‘don’t be there’), that the species is not at risk, although individuals may be. To look at it another way, if a volcano could wipe out a species, it would already have done so and it is unlikely that that species would have had time to evolve.

It has been different in the past. The Permian extinction came close to sterilising much of the globe, and it was due to the massive flood basalt of the Siberian traps. A major flood basalt is not as harmless as a typical VEI6 or even VEI7 eruption. Dinosaurs were hit by a double blow, one of which came from above (Chicxulub) and one from below (the Deccan traps). They were unlucky. But few species experience anything more than a VEI7: flood basalt eruptions, like asteroids, are few and far between.

But in our modern world, species are not as robust as they used to be. Habitat is disappearing, and food sources have become depleted. The large majority of the animal carbon biosphere is now taken up by humanity and their cattle, leaving little for anything else. The amount of wild animal life (measured by mass) is rapidly decreasing. A species that used to exist over a large area may now only be found in one small area. And that can put it at risk of the unexpected. An inconvenient volcano, even a dime-a-dozen VEI4, could push it over the edge and into the eternal abyss of extinction. As the British say, it would be like Dunkirk without the boats. (Germans, of course, would need to find a different expression.)

Darwin’s frog

It is not much larger than a coin, and isn’t much to look at. But this tiny frog is special enough that David Attenborough picked it as one of ten chosen species to be in his imaginary anti-extinction ark. Part of the interest comes from history: how many animals can claim to have been discovered -and drawn- by Charles Darwin? The answer is, of course, quite a few, but it is not easy to find out exactly how many! Darwin’s Galapagos finches are not included: they were already known, and in fact it was a local inhabitant of the Galapagos who told Darwin that his finches with different beaks each came from a different island – Darwin, not familiar with the area, had not realized this. It is easier to know how many species have been named after Darwin: the total stands at 301 (including a lot of insects). Darwin’s frog has the distinction of being on both lists. Charles Darwin discovered it in December 1834, in the evergreen rain forests on Chiloé island, Chile, on his second visit there. He did not like the place, because (as he wrote), it never stopped raining! It didn’t bother the frog.

Darwin’s frog lives happily in these temperate rain forests of southern Chile. Darwin’s rain comes from the perpetual stream of low-pressure systems of the roaring forties, which hit the Southern Andes mountains and have the water (lots of it) squeezed out of them. Darwin described the difficulties of traveling in the area: walking through the forest meant climbing through and over fallen trees, many of which would disintegrate under your feet making you sink knee-deep into the rotten wood. He wrote how the trees and vegetation were so thick that their feet hardly ever touched the ground. These dead, (glorious) fallen trees, fully covered in moss, made much of the area impassable. They finally gave up and returned to the trenches Beagle.

In this green tree morass, the frog hardly stood out. It is tiny, at 3 centimeters across (just over one inch, if your metrics doesn’t use metrics). The green and/or brown colouring provides superb camouflage, to the point that the only way to see the frog, even when standing next to it, is when it moves. The colouring is variable: seen from above it can range from uniformly green to uniformly brown, and anything in between, but it fits the boggy surroundings covered in moss and dead leaves well: it looks much like one of those leaves. The underside of the frog is very different, and is a mess of black and white blotches. When threatened, it turns upside-down, shows this black-and white underside, and plays dead; it may also jump in the stream and do the same while floating. But it has one disadvantage in the hiding game: it is loud – at least the males are. The frogs are diurnal, but the males sing at night, mainly in the breeding season which runs from October to March. And it is these males who show extraordinary behaviour. They incubate the live-born froglets in their mouth (the vocal sacks, to be precise), and spit them out only when they reach 1 cm in size. It shares this behaviour with sea horses, but no other land-based vertebrate does this. Imagine, carrying 10-15 froglets inside you each of which is a third of your body length! All the internal organs have to move out of the way – and imagine the wriggling! The male must be so glad to finally be rid of them. The froglets have no gills and absorb secretions supplied by the male inside its vocal sac: they could not survive outside the mouth of daddy. It is a well evolved, but very rare, evolutionary strategy.

Unlike Darwin, this frog really likes humidity. It lives along slow, cool streams (temperatures between 5 and 20 C) and in forest bogs where the humidity never drops below 70%, in the evergreen rain forests of southern Chile and nearby Argentina.

A surprise was that Darwin’s frog turned out to be two different species: Rhinoderma darwinii  (the southern Darwin’s frog) and R. rufum (the northern Darwin’s frog). The latter has not been found in the wild for considerable time, and is now believed to have gone extinct around 1982. It was only recognized as a separate species in 1975, so its independence (frexit) was short-lived. It differed from R. darwinii in a few aspects, including a more northerly distribution and the fact that it incubated only to the larval stage whereas R. darwinii waits until the larvae have become froglets. But R. rufum is no more, and R. darwinii is only found in severely fragmented populations. Originally, they were found along the entire southern Chilean coastal forest. Much of this original forest no longer exists, ands has been replaced by pine and eucalyptus plantations. This certainly contributed strongly to the decline, as all surviving populations are in native forest. But Darwin’s frog is also in rapid decline in protected parks and reserves. By 2010 only around 60 fragmented populations were known, each counting no more than 100 individuals.

There has been an illegal pet trade in Darwin’s frogs, mainly to the US, and together with the disappearance of its natural habitat this will have contributed to the disappearance of some populations. But the fungus which has devastated amphibians elsewhere has been found in the remaining populations and it is believed to be a major cause of the high mortality. The fungus is Batrachochytrium dendrobatidis, and the fatal disease it causes is called chytridiomycosis. The decline of Darwin’s frog has also occurred in places which are inaccessible and have little human impact, which suggests that this fungus may be to blame. At the current rate of decline, Darwin’s frog could be extinct within 15 years, after which no land-living mouth-brooding vertebrate will have survived.

But there is another aspect. It lives in an area peppered with volcanoes. One can imagine that a frog which likes a bog does not enjoy ashy and pyroclastic eruptions. And this area has had two major eruptions which coincided with the frog’s decline, only a few years apart. Is it possible that this is one species at risk of volcanic extinction? The two eruptions were Chaiten 2008, and Puyehue 2011. Let’s have a look – preferably from a dry place at a safe distance.

Chaiten

The first activity of the 980 meter high Chaiten volcano came on 30 April 2008, with a series of earthquakes. Chaiten was not considered an active volcano, and there was little direct monitoring: in consequence these warnings were only noticed after the fact. The first earthquakes detected in real time followed, and 20 hours later the inhabitants of the local town (also called Chaiten, located on the coast) began to feel the quakes which now reached M5. Only four hours after the earthquakes began to be felt, at 23:38pm on May 1, the mountain exploded. The magma had moved from the chamber 5 kilometers below to the surface in only 4 hours, at almost Hekla-like speed. The stratospheric eruption column was maintained for 6 hours: it reached a height of 19 km. Afterwards, a 200-meter crater was reported.

It was a rhyolitic eruption. These are uncommon: there had been only two similar eruptions in the entire 20^th century, St Andrew Strait volcano in 1953 and Novarupta in 1912. And the explosion had come as a surprise, since Chaiten had not been active for many centuries, possibly over 5,000 years. (There was a possible eruption in the 17^th century.) Before the eruption the volcano had a caldera, 2.5 by 4 km, with a central dome. This dome exploded in the huge eruption. The Chilean government ordered a full evacuation out to 50 kilometers from the volcano. This may have saved significant lives: the town of Chaiten initially escaped the brunt of the eruption, but was later fully destroyed by lahars.

Further significant eruptions occurred on May 3-5, followed by a very large explosion on May 6 with ash to 20 km height. This event left a crater 800 meter in size. A third major explosion followed on May 7 but this was poorly observed due to the poor weather. Pyroclastic flows destroyed the 2500 hectares of forest on the northern flank of the volcano, either on May 6 or 7. These flows snapped off trees meters above the ground, but appear not to have been particularly hot as the leaves did not burn. This points at the destruction of the old lava dome as the source.

A new dome developed after May 12. This became unstable, and finally collapsed on Feb 19, 2009, with pyroclastic flows reaching 5 km away to the south. After this, minor activity continued until 2011.

The ash of the eruption was blown to the east, with each of the three main events covering a slightly different area. 65 km away, at the Argentinian border, a thickness of 30 cm was measured. Flights were disrupted over southern Chile and Argentina, and one aircraft turbine was badly damaged when flying into an ash cloud. The climate impact was limited, as the rhyolite contained little sulfur. But the ash covered a large area, as became evident from subsequent satellite images. Initial measurements came up with very high eruption volumes, but detailed measurements later brought this down to 0.5-1 km³ of ash: a high VEI4. The ash volume was not extreme for a rhyolitic explosion, but because of the changes of the wind the area affected by the ash was large. The coastal forest was little affected because of the prevailing westerly winds, but forests near Chaiten were covered in deep ash.

Puyehue-Cordon Caulle

The name needs some explaining. The volcano is called Puyehue. It has a fissure called Cordon Caulle, and together they make up the Puyehuhe-Cordon Caulle volcanic complex, awkwardly abbreviated as PCCVC. (There is even a third member of the clan, Cordillera Nevada, which has collapsed and formed a large caldera. It is located at far end of Cordon Caulle.) Puyehue is a 2.2-km high stratocone with a 2.5-km wide, 250 meter deep crater, but it appears to be currently inactive and hasn’t erupted for over a thousand years. The 20-km long ridge of Cordon Caulle, in contrast, is a frequent eruptor, with 7 recorded events during the 20^th century. The fissure has clearly managed to capture the magma conduit and is currently starving the summit of lava. One day the summit will fight back and come to life again.

It was one of the most photogenic eruptions of the 21^st century. In contrast to Chaiten, there had been considerable warning of the eruption. Because of its history, the volcano was probably well monitored. Earthquakes started late April 2011, and build up during May. On June 3, the size of the earthquakes sharply increased and the next day they reached M4. The explosion began on June 4, at 14:45 Chilean time, from a new vent 7 kilometers north-northwest of Puyehue. Like Chaiten, this was a rare rhyolitic explosion. The first plinian eruption lasted an amazing 27 hours, during which the ash cloud reached 14 km in height and began to spread eastward, reaching the Atlantic Ocean and even the now inappropriately named Buenos Aires further north. Over the next two weeks, the ash cloud circled the (southern) globe. Flights were canceled from Argentina to New Zealand, and eventually also in Chile when the ash cloud reached it again on June 18. 3,500 people were evacuated, some by force. This worked: there were no casualties, even though there were extensive (and hot) pyroclastic flows in the valleys to the north reaching 12 km from the vent. The explosions continued, and although the column now only reached 10 km, more ash was still being added to the eruption volume. An effusive eruption began on June 20: it eventually covered 7 km². The explosions continued until April 2012 but did not reach the strength of the initial eruptions.

Subsequent research identified 13 different layers in the ejecta. The total volume of the ash remains disputed. The lowest estimate is close to 0.2 km³, whilst the highest is around 2.5 km³. The ash was distributed over a large area covering much of Patagonia, and this causes uncertainties in extrapolating the total volume from individual measurements. What (to me) appears to be the best established number for the first eruption is 0.75 km³; later eruptions added about 0.3 km³, and the pyroclastic flows had a volume of 0.08 km³ which would give a total number around 1.2 km³. This was a VEI5, so far the largest explosive eruption of the 21^st century. Because the explosions lasted such a long time, changes in the wind ensured that a large area, mainly in Argentina, was affected. The deepest ash layers were 50 cm thick.

Living with ash

Volcanic eruptions can be bad for wild life, but we rarely know how bad. The only one for which detailed estimates are available is Mt St Helens: The Washington Department of Game (note the name) estimated that 11,000 hares, 6,000 deer, 5,200 elk, 1,400 coyotes, 300 bobcats, 200 black bears, and 15 mountain lions died during the eruption. The one volcanologist who sadly died whilst observing the eruption, David Johnston, was not listed. The impact on frogs was also not listed, probably because (like volcanologists) they are not a well-known game species. The later effects of the ash were not included in the numbers. Volcanic ash is known to cause silicosis, resulting in lung impairment and scarring. Eyes can also be damaged. Sulfur gases associated with the ash are dangerous, with birds particularly sensitive, and water-based animals can be affected by acidification of pools and streams. After an ashy eruption, little vegetation is left and the remaining animals can face starvation. Thinner ash layers are mainly a problem for deeper grazing animals such as sheep and deer. Cattle tend to go for top growth and are less affected, but deep ash layers are problematic for both. Volcanic ash can also cause fatal gastrointestinal blockages. The sharpness of the ash particles can kill insects, and this affects the animals feeding on them, including birds – and frogs. Ash is not good. The final wild-life toll of St Helens must have been considerable higher than those caused directly by the eruption.

Regarding Chaiten and Puyehue-Cordón Caulle, rhyolitic eruptions tend to be sulfur-poor, so for both Chilean eruptions the ash itself was the main danger, both from direct and indirect effects. Large rhyolitic explosions are not all that common, so having two in close proximity within a few years is a notable event. The rhyolitic ash of both eruptions was somewhat different. Puyehue-Cordón Caulle had the most significant impacts, not only because it was a bit larger with a larger depth of the ash (sufficient to kill forests) but also because of a high fluoride content of the ejecta. In addition to the effects listed above, sheep, horses and cattle succumbed to fluorosis; it may be expected that wild animals were also impacted. Frogs are known to be sensitive to fluoride: in New Zealand, native frogs developed osteofluorosis after being exposed to fluoridated water.

Frogs that live in moss-covered forests with eternal rain may have trouble living in ash instead. Deep ash kills the vegetation they rely on, but also lowers the humidity as the rain which used to be caught by the vegetation now quickly drains away on the ash. This is a temporary problem: over time, the vegetation recovers and the ash becomes a fertilizer, but that may take several years. Plummeting insect population remove the major food source. Darwin’s frog has the additional problem that it is not a mover. The frogs stay within a kilometer or so of the same area, which is one of the reasons the populations have become so fragmented. When an area becomes unsuitable, the frog doesn’t move on – it dies out. In due course it may be replaced (slowly) from populations surviving elsewhere, but with such poor migrators that takes time and it requires that these other populations exist and thrive.

One of the remaining R. darwinii populations was located 22 km south-west of Chaiten. In the year after the eruption, the frog was no longer recorded there: it had not survived the eruption. There were two populations near Puyehuhe-Cordon Caulle: one of these disappeared completely. The westerly winds helped the frog, as it blew the ejecta away from the coastal forests. But some of the few surviving populations were too close to be saved by the wind.

Future of the frog

Darwin’s frog, at least the surviving one of the pair of species, is highly threatened. The rapid removal of their natural habitat probably initiated the decline. The volcanic eruptions have not helped, and have reduced the range of Darwin’s frog further. But the dominant threat is currently the spread of chytridiomycosis. Mortality among the young due to the chytridiomycosis disease can reach over 50%. Models show that this will lead to extinction of small populations. Infectious diseases normally die out before the species that acts as their host can go extinct, but this fungus does not obey these statistics, because it has other hosts available.

Chytridiomycosis was first found in Queensland, Australia, in 1993, but was already rapidly spreading around the globe. The disease is now believed to have entered Chile already in the 1970’s. How it arrived is not known, but the main suspect is the African clawed frog which appeared around this time. It was imported because at the time it was used in pregnancy tests: a bit of urine was injected into their hind leg, and if this caused the frog to lay its eggs, the urine was from a pregnant woman. In the 1970’s, better and simpler tests became available and hospitals released their African clawed frogs into the wild. The discovery that these African frogs carried chytridiomycosis, without themselves being negatively affected, came in 2006. It would be sobering if those old tests for human reproduction were indeed the cause of the current wave of amphibian extinctions. One third of all amphibian species are under threat, and in Panama alone 100 different species may already have been lost. This is truly the revenge of the frog.

The fate of Darwin’s frog has become well publicised, by David Attenborough and others. Action is being taken, and several captive breeding programs were started in Chile during the ‘year of the frog’ in 2008. The frogs do breed in captivity but are just as susceptible to chytridiomycosis: an early attempt to breed the frogs in Germany reportedly failed when all 30 frogs died from this infection. Attempts are continuing: http://reportagen.frogs-friends.org/en/darwins-frog/cooperation. A collaboration between Concepcion and Leipzig has been particularly successful. But not without problems. Five European zoos worked together to obtain viable groups of Darwin’s frogs, but during the wait for export licenses (a long process for endangered species), in 2016 a disease affected the Concepcion program leaving only 20 surviving frogs. The disease was finally eradicated in 2017, and as of autumn 2018 the wait was still on for enough young frogs to grow up to try again for export licenses.

Darwin’s frog is now red-listed as threatened with extinction. Small populations can be at risk of many factors and the final cause of extinction may be an accident – a bad storm, a forest fire, or an eruption. The decline makes them vulnerable. In this way, the two large eruptions contributed to the threat of extinction: they have removed 2 or 3 of the remaining populations. Under normal circumstances, the frog would happily have survived elsewhere and over time repopulated the devastated areas. That recovery is not an option under the current circumstances. The resilience isn’t there.

But could previous volcanic eruptions have had any significant effect on Darwin’s frog? That is very difficult to know, especially with an animal that fossilizes rather reluctantly. It turns out that there have been many previous eruptions, and the 2008/2011 events were not particularly large for the area. There are many older tephra layers around Puyehue, and some are surprisingly recent. Five such layers (pre-1900) date from the holocene and are post-glacial. They range in thickness from tens of centimeters to 1-2 meters. The layers are dated at 10.5 ka BP, 7 ka, 2.5 ka, 1.9 ka and 1.1 ka. The last one erupted between 1.7 and 3 km³ (DRE) from Puyehue, 2 to 3 times larger than then 2011 eruption. The 1.9 ka event (dated to 1932+-68 BP) was the largest of the series, at 8 km³ DRE. It did not come from Puyehue but was from the Antillanca volcano, 20 kilometer south where it formed a 4.5-km wide caldera. (Antillanca caldera is now home to a new volcano, called Casablanca. It is one of the fastest growing volcanos in the southern Andes.) Eruptions with volumes near the 1 km³ mark may be quite common: they happened here in 2011, 1960 (triggered by the M9.5 earthquake) and in 1921. But all five layers listed above are larger than this.

The Chaiten area similarly shows evidence of past, large eruptions. There is a second volcano in the area, Michinmahuida, located 20 km east of Chaiten. It differs from Chaiten in its composition: whereas Chaiten produces rhyolite (it is the only volcano in its surroundings to do so), Michinmahuida produces andesite and dacite. Both volcanoes have produced holocene ejecta blankets. The most significant one is the Amarillo ignimbrite, dated to 10.5 ka BP, and reaching a thickness of 80 meters. This eruption may have formed the Michinmahuida caldera. The tephra volume (non-compacted) is 10 km³ at minimum. The main ignimbrite is only found around Michinmahuida but it appears to be associated with tephra layers elsewhere, including on Darwin’s least-favourite island, Chiloé, the stronghold of the frog named after him.

Michinmahuida had another eruption around 7.3 ka BP, producing around 2 km³. The Chaiten eruption at 9.5 ka BP left tephra layers 70-cm thick, and indicate a tephra volume of 5.5 km³. It was followed by one around 4.5 ka BP which may have been two separate events, producing 4.7 km³ of tephra and leaving meters-thick pyroclastic deposits. There may have been another eruption similar in size to the 2008 event which has been dated to the 17^th century.

The conclusion is that both locations have shown eruptions much larger than those of 2008 and 2011. These must have devastated much of the surrounding area. They clearly did not lead to extinction of Darwin’s frog, but locally, they would have had a significant impact. One can speculate whether a very large eruption could have lead to to the separation of the northern and southern Darwin’s frog into two different species.

What is the future of Darwin’s frog? It looks bleak. The only hope appears to be either a disease-free and long-term funded captive breeding program, or the evolution of the fungus into one that is less lethal. Neither hope seems well founded. If the models are correct, we could loose the only land-based vertebrate mouth-breeding species within 15 years. There are volcanoes in the area which could give it its final push over the edge. But it looks like those won’t be needed. For this frog, extinction is happening too fast already.

Volcanoes do not make species extinct. On the other hand, they don’t need to. We can do it quite well without their help, and with no one else to blame. Darwin opened for us the book of evolution. It is filled with wonders. One of those wonders could be about to disappear, and it may never re-evolve. In Darwin’s cafe, is it time for last orders?

Albert, February 2019

References:

The Population Decline and Extinction of Darwin’s Frogs.
Claudio Soto-Azat ,et al., 2013, PLoS ONE 8(6): e66957. https://doi.org/10.1371/journal.pone.0066957

Cryptic disease-induced mortality may cause host extinction in an apparently stable host–parasite system. Andrés Valenzuela-Sánchez, et al. 2017, Proceedings of the Royal Society B: Biological Sciences, 284 (1863): 20171176 DOI: 10.1098/rspb.2017.1176

Complex dynamics of small-moderate volcanic events: the example of the 2011 rhyolitic Cordon Caulle eruption, Chile. Marco Pistolesi et al., 2015, Bulletin of Volcanology 77:3. https://link.springer.com/article/10.1007%2Fs00445-014-0898-3

Holocene tephra succession of Puyehue-Cordon Caulle and Antillanca/Casablanca volcanic complexes, southern Andes. J.A. Naranjo et al. 2017, Journal of Volcanology and Geothermal Research, 332, 109-128. https://www.sciencedirect.com/science/article/abs/pii/S0377027316301986

Holocene record of large explosive eruptions from Chaitén and Michinmahuida Volcanoes, Chile. Álvaro Amigo et al., 2013, Andean Geology 40: 227-248. http://www.andeangeology.cl/index.php/revista1/article/viewFile/V40n2-a03/pdf