The Basel earthquakes

Late in 2020, an M6.4 earthquake struck the town of Petrinja in Croatia. It caused extensive damage in the town and in nearby villages, and 7 people died. Even so, the impact was more limited than it might have been because houses here tend to be well build. It came as a surprise: powerful earthquakes are infrequent here. But there was precedence. A similar event had taken place 140 years earlier 30 km away, in Zagreb.

140 years is a long time. People don’t remember what neither they nor their parents have seen. It is not part of their living memory; events 5 generations ago seem an irrelevance to our lives. History is forgotten until it is repeated. Isn’t this true of the current pandemic as well? Current events are almost a copy of the 1918 Spanish flu, spread from the US by the movement of soldiers across the world. We had forgotten.

Petrinja is not a large town. It is important only to those who call it home. It is an Anatevka, a small place within a much larger world. Anatevka is the fictional shtetl (Jewish township) of Fiddler on the Roof. The movie and the musical that came before were based on Sholem Aleichem’s story, Tevya the milkman. Tevya and the other people who live in Anatevka are subject to powers outside of their control, forbidden to move and suffering frequent progroms. They are strangers in a strange world, subject to every whim of the home office. The lack of power of the local people is described brilliantly in the movie: “If the rich could hire others to die for them we, the poor, would make a nice living”. The movie is about how tradition imparts stability to their powerless lives. As Tevya says, “without traditions our lives would be as shaky as a fiddler on a roof.” But tradition also causes inflexibility, and when the pressure grows something has to give. Tevya begins to see how traditions have to change with the times. “Our old ways were once new, weren’t they?”. He manages to break free of part his own traditions, but Tevya is unable to complete the journey. His world remains shaped by history and traditions. The movie was so successful because it is true to our own lives. All of us live in a world shaped by culture and parents. We see the world through highly coloured glass, and this gives comfort and stability. It is what makes volcanoes so difficult to live with: they can change our world irreversibly, and without warning!

Traditions seem forever, but in reality are rarely more than 2 or 3 generations old. The world changes too rapidly for that. An earthquake 140 years ago leaves us no traditions. They do leave stories. Stories can long outlive traditions, and pass on knowledge from a world lost to memory. Stories can last thousands of years. But without context, their meaning becomes lost and the stories no longer carry a warning.

Although Anatevka is sited in the Ukraine, Fiddler on the Roof was actually filmed in Croatia. The Anatevka of the movie is Lekenik, just 15 kilometers from Petrinja, halfway to Zagreb. In fact, Lekenik lies midway between the two most damaging earthquakes in Croatia of the past centuries. When the earth moves, people have to move too.

An earthquake in Anatevka would not have left lasting effects. The fictional town was created to be insignificant. An earthquake in a capital city would be a different story. Petrinja reminded us that one of Europe’s capitals, Zagreb, once suffered a damaging earthquake. But is this unique? Which other cities in Europe could be in danger?

Earthquake risk in Europe. The colours indicate the maximum ground acceleration expected over 500 years, with 1g as maximum. Source: https://www.e-periodica.ch/cntmng

There are obvious candidates. Turkey’s capital Istanbul has a history of major earthquakes. Portugal’s capital Lisbon was once destroyed by an earthquake that caused the economic collapse of its empire. The worst earthquake known in European history was in Messini in southern Italy, as recent as 1908: it left over 50,000 dead. Naples is at risk, but Naples is at risk of many things. The locals seem not to worry about. I love the city and its people but despair about their attitude. Cyprus is at risk of major earthquakes. So far, all well-known and recognized localities – and all are on the coast. But there is another place like Zagreb, deep in-land, far from obvious fault lines but with a shaky history. And unlike Zagreb, it was destroyed by earthquakes not once but twice. Welcome to Basel.

Basel

Perhaps this is the most international city in the world. It lies on the river Rhine, and has a foothold in three different countries. The city itself is in Switzerland, but it has suburbs in both France and Germany. Each of the three countries has its own railway terminal in the city centre. The city has 180,000 inhabitants; over 800,000 people live in its vicinity. Basel has a reputation as a very livable city, at least according to the wikipedia article which seems to have been written by the Basel advertisement agency. The article only mentions one earthquake, and does so only in passing. Some things are best forgotten.

The city started out on the southwest side of the Rhine but it now is on both sides with five bridges; the oldest bridge dates from 1255. Basel is located where the Rhine makes a 90 degree turn and begins to flow north, in between the Vosges and Black Forest mountains. The story of the city is closely linked to that of the river.

The oldest of the 5 bridges

Rhine

The Rhine links the Alps to the North Sea (click here for full, readable resolution). It is the main trade route north for Switzerland and Germany. The Netherlands owes its very existence to it: the country is largely the delta of the Rhine. At one point the Rhine was the northern border of the Roman Empire – an attempt to put the Roman border at the next river across did not fare well. The river remains a borderline to this day: it forms four international boundaries involving five countries. The upper reaches flow from the Alps to Lake Constance. After the lake, it becomes known as the High Rhine. At Basel it turns north, and the next stretch is the Upper Rhine. Later it becomes the Middle Rhine, the Lower Rhine and finally the Neder Rhine. Everyone wanted to name their own stretch. The last major diplomatic incidence in western Europe was when France decided to dump salt in the river, knowing full well that it was used for drinking water downstream. Rivers both connect and divide.

The Upper Rhine between Basel and Frankfurt follows an old rift valley. The Upper Rhine graben is 300 km long and 30-40 km wide. Strasbourg, one of the sites of the European Parliament, is in the middle of the rift. It is an extensional basin, and part of a larger, segmented old rift system that extends as far north as Oslo.

The rifting of the Upper Rhine graben was caused by the stress from the uplift of the Alps, and to a lesser degree by that of the Pyrenees. This happened something like 40 million years ago; the rifting mostly ended 30 million years ago but some movement continued until much later.

The basin has mountain ranges on either side, the Vosges and the Black Forest. The mountains are much younger than the graben. There are linear, segmented boundary faults on either side: the western Rhine Fault zone along the Vosges, and the eastern Rhine Fault zone along the Black Forest. The rift ends near the southern German border. South of it are the Jura Mountains, a beautiful linear chain along the Swiss-French border, a crumple zone pushed up by the Alps.

Basel lies just south of the Rhine graben and the Black Forest, southeast of the Vosges, and just north of the Jura. It has a view to all of these. But the view can spell trouble, as the Roman settlers soon found out.

AD 245

Having an empire is nice. It is good for your ego. It is less good for your security. It needs a lot of defending. Everyone wants a piece of the empire’s cake. Some see easy pickings for a raid. Others want their own empire. Some just want their original home land back. Some just want to trade. Some are looking for work, and others may be fleeing the chaos outside the empire. The natural solution is to create a buffer zone, but then you have to defend the buffer zone as well and that creates a new border on the other side, and so on. The Roman empire had a range of strategies to deal with the troublesome outsiders. They chose natural obstacles for the location of the border, made alliances with tribes near the border, and of course had a large army. They even build a wall. The most successful strategy turned out to make the outsiders insiders, and hand out citizenship. It created a land of the free, and gave people a reason to defend their inner freedom.

Emperor Augustus handled his border problems rather well. To keep the pesky northern Europeans (also known as barbarians) at bay, he had a scheme to secure the Alps as his border zone. Augustus ordered the development of three fortified settlements, located along the primary access routes into the empire. They were placed along larger rivers which were difficult to cross. It is hard to invade if your army can only get across in a small boat, one by one! to control the main river crossings. This channeled the outsiders to particular river crossings where the forts were waiting. The three settlements were Augusta Praetoria at Aosta (south of the Alps), Augusta Vindelicum on the Danube (at Augsburg), and Augusta Raurica on the Rhine. A certain ego-centricism may be noted in the naming. ‘L’etat, c’est moi’, he could have said had he known French.

Augusta Raurica was located on a river terrace on the southern side of the Rhine, 1 k from the river and 20 km east of modern Basel. The ‘Raurica’ name was local: this was the homeland of the Celts, and the Raurici were a Celtic tribe in a border alliance with the Romans. Augusta Raurica was in existence by 15 BC. The city overlooked the Rhine, was backed by the Jura mountains and had two small rivers on the west and east side. It was a very well devised defensive location. It was also a crucial location for traffic, as the main route through the Rhine graben ended here. Augusta Raurica became much more than a fort. It quickly grew to become a wealthy trading centre with a population of 20,000. The amphitheatre could seat 8,000!

But although it was well defended against enemy armies, it was not as secure against mother nature. Nature went on the attack when a powerful earthquake hit the city. It has been dated to between 245 and 255 AD. Interestingly, there are no written reports known of the earthquake. It is known solely from archeology. Excavation revealed devastation. There were many ruined buildings, collapsed columns, toppled section of walls with human skeletons underneath the rubble. Some quick repairs had been attempted, but these seem haphazard and they give the impression that effective government collapsed after the disaster that befell Augusta Raurica.

From Faeh et al, 2006, J Seismol 10:459–477

The earthquake left the city vulnerable. German tribes attacked the region in the summer of 260 AD. The Roman consul of Galicia defeated them, but not before they had destroyed what remained of Raurica (perhaps aided by rampaging Roman troops). The consul in question, Postumus, was an able but ambitious person with one eye on becoming emperor. The normal path to this was to take over a province, and take it from there. Postumus followed this route: after the battles left him in full charge, he broke away from the empire in 260 AD and ruled (quite ably) over modern France, Spain and Britain. This was bad news for Raurica. The ancient brexit stopped much of the trade on which Raurica had depended. In one triple blow, the city had lost its buildings, its security and its wealth.

The break-away territory became re-incorporated into the Roman empire by 274 AD, after the death of Postumus who never became emperor. This was too late for Raurica, and the city did not recover. Instead there was rebuilding in two nearby locations. A new fort was build: the location remained strategically important. But the wealth was drained from it and the population now lived in poverty. It takes peace to build prosperity. When the Roman empire vacated the area in 400 AD, the tribes that took possession occupied the two settlements. Over many centuries, these survived and eventually became the modern towns of Augst and Kaiseraugst. But all that remains of Raurica is an archeological site and a museum. It is a pleasant place to visit: the ruins are located within a park, with a trail that connects the various remains. But it is a walk into the past. After the earthquake, Augusta Raurica became history.

There is a pattern here. A single disaster is survivable. It becomes a drama when two (or in this case three) disasters hit in quick succession. The earthquake caused massive destruction, but it wasn’t irrecoverable. The recovery failed because of unrelated political events. It was an earthquake with bad timing.

How strong was the earthquake? A value of M6.9 is sometimes given (moment magnitude) but this has been questioned for several reasons. First, an event this size would have been felt wide and far, and one would expect that it was mentioned in multiple written documents from different locations – none are known. Second, one would expect earthquake scars in the landscape, but little has been found. (There is one sign: a fallen block of lime stone in the Battlerloch cave, 10 km southwest of Raurica, has been dated to approximately this period.) Third, the destruction was localized. The city was divided into the upper town and the lower town. Uptown was the centre with the major buildings, whilst downtown was where the workers lived. The recorded damage is only evident in the uptown: downtown shows little evidence for destruction.

(There are two provisos here. The downtown buildings were much more basic, and frequent rebuilding might have been required here anyway. This makes it difficult to assign any particular damage to the earthquake. And because Roman remains of this time are not common in the area, wider damage may have been missed.)

The difference in location between the upper and lower town is important. Uptown was build on the terrace overlooking the river. Downtown was build on a 10 meter thick layer of gravel. It turns out that the terrace amplified the shaking whilst the gravel did not. Thus, the uptown was subjected to a stronger quake than downtown. The rich came off worse. This amplification leaves the strength of the earthquake in question. An M6.9 may indeed not have been needed: models suggests that a much weaker but local earthquake could have caused the severe damage to the town. An M5.9 or M6.0 may have sufficed to end the story of Augusta Raurica.

AD 1356

While the Roman settlement of Augusta Raurica flourished, a nearby different settlement also existed. There had once been a Celtic village near modern Basel. Around 80 BC this unfortified settlement was abandoned and the people moved to cathedral hill (inside the modern city), protected by the Rhine and the river Birs, as well as by an earthen wall. Clearly, the settlement was experiencing raids and the people needed a better defense.

During the Roman era the main settlement was in Augusta Raurica, but apparent a separate Roman garrison was stationed at cathedral hill. It is not clear whether that included a fort, as is often claimed. After the destruction in Raurica the stability of the second location became an advantage. Emperor Valentian stayed here in 374 AD, and at this time the settlement was first called Basilia. Further development was slow and the settlement remained small. It overtook Augst (new Raurica) only when a long-distance road was developed in the Birs valley, around the 7th century. This left Basilia much better connected to civilization, i.e. to southern Europe. From here on, Basel would become the dominant town in the region.

By the 14th century Basel had grown prosperous, and cathedral hill had acquired a cathedral. It remained smaller than the old Roman town of Augusta Raurica had been: the population at this time was perhaps 10,000. Now, an eventful era came. In the summer of 1338, grasshoppers devoured the harvest. In July and August 1342 flooding reduced the harvest again. From 1345 to 1347 terrible weather caused famines. In 1349, the Black Death hit the city, with as side effect attacks on the local Jewish population who got the blame. In 1354, Basel was partly destroyed by fire. These were fairly typical disasters for a medieval town, but rather a lot of them happened close together.

The next one was not typical. On October 18, 1356, an earthquake swarm hit. The first jolt happened just after noon, soon followed by two weaker shocks. Around 5pm there was a stronger shock which caused people to flee their houses. That turned out to be a good thing. At 9pm a much bigger earthquake struck. This remains the strongest historical European earthquake known north of the Alps.

Source: wikimedia

Basel was now in a bad state. Reports state that it was utterly destroyed, but that should be taken with caution. Similarly, wikipedia’s claim that there was destruction from Paris to Prague badly misquotes its reference which only states it was felt in these locations. But the damage was major. The cathedral on the hill lost all five of its towers, and the nave vault collapsed. Two towers and the vault were later rebuild; of the other towers only some corner stones remain. Other churches were damaged. Many buildings lost their roofs, and walls were cracked throughout the city. A number of castles were destroyed, but we don’t know how many: various documents give numbers varying from 20 to 60. As an example, Madeln castle outside of Basel collapsed and was never rebuild. The ruined castles appear to have been located mostly south and southwest of Basel, 5-15 km away. Some buildings in Basel survived without major damage: of the 63 buildings that still exist in Basel which contain structures that date from before 1356, six show no indication of rebuilding or restoration from this time. But many of the oldest buildings were damaged, often severely. The buildings were those with irregular construction, thin walls and/or many openings in the walls. The strongest buildings included one monastery which indeed survived with little or no damage. Building standards matter.

It is not known how much of the destruction came from the 5pm quake and how much from the 9pm but it seems likely that the latter did most of the damage. The earlier earthquake may have helped to limit the number of casualties. There is no authorative number for those. Around 8000 people may have lived in the city and the surroundings after the black death: based on this, the number of 300 dead seems plausible, and the number of 2000 listed in later documents very unlikely. But contemporary records only name three people who died.

There was some damage in other regions. Bern, 80 km from Basel, lost a church tower, and had cracks in the city walls. North of Basel the earthquake was felt in Strasbourg. A church tower reportedly collapsed in Besancon, 100 km west of Basel but this report again should be taken with caution. The earthquake was felt at least 200 km away. But the majority of the destruction was in Basel, and the epicentre was likely near the city.

After the earthquake came the fire. This is common after destructive earthquakes, in modern times because of damaged gas lines, and in medieval times because of the open cooking fires in combination with straw roofs. The fire swept through the buildings inside the city walls, and affected especially a poorer region of the city.

Building construction changed after the earthquake. Much more use was made of brick: the fear of the shaking ran deep. But the city was not abandoned. Unlike Augusta Raurica, it was rebuild and Basel continued to prosper in its old location.

Modeling of the damage to buildings indicates that the earthquake had intensity IX. The Mercalli scale defines this as:

IX. General panic. Weak masonry destroyed; ordinary masonry heavily damaged, sometimes with complete collapse; reinforced masonry seriously damaged. Serious damage to reservoirs. Underground pipes broken. Conspicuous cracks in ground. In alluvial areas, sand and mud ejected; earthquake fountains, sand craters.

This corresponds to a surface acceleration of 0.5 to 1g. This intensity can be achieved at the epicentre of earthquakes of magnitude 6 or 7. The shaking strongly depends on local conditions and depth of the earthquake. Opinions differ on what the actual size was. The lowest estimate is M62, a common one is M6.6, but modeling of the buildings in Basel that date from before 1356 has suggested a moment magnitude between 6.7 and 7.1.

Other events

There are other reports of earthquakes in the Basel region, albeit less destructive. Not all reports are reliable: a large earthquake in 1021 is mentioned in 16th century writings, but we know from other documents that it occurred in Bavaria on Friday, May 12, and there is no indication that it affected Basel in any way.

A significant earthquake in 849 is mentioned in several monastery annals as a ‘terrae motus’. The event happened in the early morning of Saturday April 20; the aftershocks continued until June 1. It was reported in Reichenau, well east of Basel in the Rhine valley near Lake Constance. But there is no evidence that it affected Basel.

Other but weaker earthquakes have been reported in Basel in 1357 (likely an aftershock), 1428, 1572, 1610, 1650, and 1682. The Mercalli intensity of these reached VII, corresponding to perhaps magnitude M5.5. Such an earthquake can damage poorly constructed buildings and bring down chimneys, but it should not cause major damage. But after 1682, all went quiet. Nowadays the region has earthquakes of M4, but the larger ones of the past have long been left behind by living memory.

Large earthquakes should leave a memory in the landscape,. One may expect disturbed sediment layers in lakes. Indeed, five earthquake-induced layers have been found by drilling into local lakes. They occured after 12,000 BC: before that time the ice-age glaciers still ruled. The assigned dates are (approximately): 180–1160 BC, 2900–3850 BC, 4870–5660 BC, 8260–9040 BC and 10,720–11,200 BC. The reason for the fairly large uncertainty on the dates is that sedimentation rate in the lakes is very low, at 1 mm per year. The dates are based on radiocarbon dates of material just below and just above the disturbance, and a small offset gives a large difference in time. Earthquakes of the past 2000 years are not easily detected, both because of the slow sedimentation rate and because of human disturbance. One lake was even drained 700 years ago, an unexpected scientific setback.

These older events are expected to be similar in size to 1356. Together with the 245 AD and 1356 AD earthquakes, this indicates 7 significant earthquakes in the past 14,000 years, or a recurrence time of two thousand years. One should be careful with this phrase. It is reasonable to assume that we will need to wait this long for the next one if all earthquakes happened on the same fault: it will take this long to build up enough stress. But if multiple faults are involved, then an earthquake can happen at any time and talking about a recurrence time gives a false sense of security. In that case it is is better to just state it as seven big shakes in 14,000 years, or a chance of 1 in 20 per century.

Faults of Basel

The builders of Basel were no aware how faulty the region was. There is quite a choice regarding the fault or faults that caused the two large earthquakes.

Source: K. Ustaszewski, S. Schmid, 2007, Bull. angew. Geol, 12 https://tecto.earth.unibas.ch/Members/Schmid/Publications/104_Ustazewski&SchmidBullAngGeol2007.pdf

The tectonics in the area is dominated by two big structures. The Rhine graben has already been mentioned. It runs north-northeast from Basel, and with fault zones on both side of the graben. The zone on the west side, bordering the Vosges, is quite far from Basel and is probably in the clear. The fault zone on the east size, bordering the Black Forest, is much closer with two of its faults on either side of Basel. This has always seemed the most likely cause, but there are problems. The faults have notable escarpments north of Basel, but escarpments are not visible around Basel or further south. There is little evidence that these faults are active closer than around 20 km north of Basel. And the northern region seems excluded for the Basel earthquakes. The destruction of castles happened mainly south of Basel: only two of the ruined castles were located in the Black Forest.

This moves the attention to the Jura. It is a classic thrust-fold structure, where the surface has been pushed up and forward, forming folds. Blame Italy for this – the Jura are forced by the Alps which are forced by Italy wanting to join Europe. It is the geological version of the Roman empire! The layer that is on the move consists of Jurassic (there is a clue in the name ‘Jura’) sediments that lie on much older rock. The base rock isn’t moving: the sediment has detached from it. The detachment fault lies a few kilometers deep.

The Jura has been thrust against the Rhine valley, and it is the cause of the 90 degree bend of the Rhine. If it moves much further it could cut off the upper Rhine from its head waters. If it is still moving. Could this thrust fault be responsible for the 1356 earthquake? It lies in the area of the likely epicentre. But the detachment is quite shallow here and any major movement should have left signatures at the surface. None are seen. River beds show some discontinuities which indicate there has been some movement here in the past few million years – but hardly enough to worry Basel.

A third option is that the basement rock itself has failed. It also is under pressure from the Alps, and it dates from an older era of mountain building which may have left ancient faults. These may have been re-activated by the Alps. However, there is no evidence for uplift associated with such a fault.

From Ferry et al 2005. https://doc.rero.ch/record/289518/files/160-2-554.pdf

A fourth option is that the cause of Basel’s demise was the very valley that once gave it its future: the Birs river valley. The Birs is the main river running north from the Jura, running through a notable valley to Basel where it becomes a tributary to the Rhine. The main town along the Birs is Reinach. The valley has an escarpment on the west side that could indicate an active fault. Investigations along this escarpment have shown evidence for recent movement with a total uplift of 2 meters. The uplift happened in three different events: the most recent has a C14 date between 610 and 1475 AD, not inconsistent with the 1356 event. The landscape indicates that over the past 250,000 years, there has been 35 meters of uplift along the fault.

The visible part of the Basel-Reinach fault is too short (8 km) to explain an M6.5+ earthquake, but the fault may extend underground, south underneath the Jura, and north underneath Basel. This would give a maximum length of 15 km. It lies in the direction of the Rhine graben and may be connected to it. It is a strong candidate for the Basel earthquake!

The escarpment near Bruderholz, a hill and Basel suburb known mainly for a battle between Swiss and Swabian troops – in 1499! The Swiss won (which is probably why this battle is remembered – our memory is much better for success than for failure). The Swiss battled raiders, but to be fair they had been raiding themselves and were on the way home when meeting the invaders.

Reinach memory

The Basel-Reinach fault is a plausible cause for the 1356 Basel earthquake. But the other faults have not been ruled out. And if the Basel-Reinach fault extends over the full 15 km, it intersects the other faults. A failure of multiple faults cannot be excluded. The fact that there were multiple earthquakes with foreshocks in 1356 makes it possible that multiple faults were involved, in a cascade of faulting.

The bottom line is that founding a village is much like buying a house: do check for faults.

The Basel-Reinach fault comes within 7 km of Augusta Raurica and is also a strong contender for the 250 AD event. In fact, any of the discussed faults could have done it. But there is yet another option. It turns out that the terrace on which the upper town of Raurica was located has a buried graben. This SSW-NNE trending graben was recognised from borehole data: it may be related to the plethora of short faults south of the Black Forest. The graben is bordered by two faults, and the eastern fault of this graben runs directly underneath the centre of Raurica. An earthquake on this fault of M6.0 or 5.9 would have been sufficient to destroy the upper town or Augustus Raurica.

Augusta Raurica. The dashed black line indicate the border fault of the buried graben.

And the next one?

If only the Basel-Reinach fault is responsible for earthquakes around Basel, then the recurrence time is likely around 2000 years and Basel has plenty of time to prepare. Too much time, probably: politicians are not easily interested in events more than one election cycle in the future. All politics is short term. After all, the children who may be affected can’t currently vote – politicians who chase the children’s votes tend not to do well. But if more faults are involved, then the recurrence time cannot be used to predict the next event, as a different fault may fail next. In that case, the next such earthquake could happen at any time. That raises (or rather uplifts) the question: How well prepared is Basel?

A sobering assessment done in 2012 suggested, not that well. The assessment modeled an M6.6 earthquake near Basel, and predicting significant impacts:

  • Between 1,000 and 6,000 fatalities
  • 60,000 injuries
  • 1,600,000 people homeless in the short term (yes, you noticed that right: for some reason it is twice the number of inhabitants)
  • damage to half of all buildings, with property damage exceeding 50 billion of that most stable of currencies, the Swiss Franc.

Such an event could seriously damage Switzerland’s stability, serious enough to expect that the politicians will go for the political solution: decide more study is needed. After all, it may go away.

A volcano mystery

The Basel earthquake came after a difficult decade. The floods of 134 have been discussed elsewhere. The poor weather that followed was not just anecdotal: from tree rings we know that the summers of 1345 and 1346 were exceptionally cold. Ice cores have shown a sulphate peak that points at a volcanic eruption in 1345. The peak is seen equally in both hemispheres, we know it was tropical volcano.

Shortly afterwards, the black death appeared. This was not the first time: 800 years earlier, the Justinian plague which devastated Europe, came after extreme weather caused by not one but two major eruptions. Which volcano kicked off the 14th century pandemic is not known. The earthquake had nothing to do with the eruption and pandemic. It just happened at just that time.

The 245 earthquake came at the start of a bad time. The 1356 earthquake came at the end of a bad decade. Disasters rarely strike in isolation. They hunt in packs.

Stability

Let’s give the final word to Tevye, who knew something about the importance of stability and the dangers of earth-shaking events.

A fiddler on the roof. Sounds crazy, no? But here, in our little village of Anatevka, you might say every one of us is a fiddler on the roof trying to scratch out a pleasant, simple tune without breaking his neck. It isn’t easy. You may ask ‘Why do we stay up there if it’s so dangerous?’ Well, we stay because Anatevka is our home. And how do we keep our balance? That I can tell you in one word: tradition!

But tradition does not give protection. Switzerland, with its tradition of stability, should also remember its history, and should not forget its faults. It may yet be shaken again.

Albert, April 2021

347 thoughts on “The Basel earthquakes

  1. Same location with another camera looking slightly to the right. note the lava moving into the lower left corner.

    • I did say it was sneaking. It’s tricksy. And what about the hornitos hitching a ride?!?

  2. The 1453 eruption attributed to Kuwae may have actually been in 1458/59, it was a massive eruption. There was a slightly smaller one in 1452/1453 that was quite likely in the northern hemisphere.

    The Long Island/Motmot eruption somebody mentioned above is said to have taken place in 1645.
    Gamkonora was around 1673.

    There was also a mystery eruption in 1809 prior to Tambora that had to have been tropical, Putana was mentioned but it lies a bit too far south to have affected the northern hemisphere.

    I can’t help but feel a lot of these studies in the 80s and 90s need updating with fresh dating methods.

    • Randall earlier proposed these candidates:

      Mt Bromo -7.952231, 112.954483
      Unnamed caldera -6.775672, 106.951131
      Mt Dempo -4.016925, 103.123812
      Zavaritski Caldera 46.920104, 151.955223
      Vulkan Krenitsyna 49.345671, 154.715538
      Ambryn Volcano -16.249344, 168.126665
      Kunishir Volcano 44.353241, 146.251688

      But I think we can dispose of most of these right away. The two Russian ones and the other with over 44 degrees north latitude (Hokkaido area?) are too far north and Ambrym is known for its effusive, convecting lava lake and occasional large lava fountains and flows, not for VEI6+ grey eruptions. That wipes out the bottom four candidates and leaves three low-latitude southern hemisphere volcanoes, all in or near western Indonesia if my geography isn’t totally failing me. The sulfate data was compatible with a low, south latitude, so none of these can be immediately ruled out on the basis of position, and Indonesian volcanoes are a generally noisy lot prone to serious roughhousing, so eruption type doesn’t look likely to rule any of them out either.

      The other suggestion, to hunt for shallow subsea calderas, is excellent. A Krakatau type event would easily account for this, especially if it were somewhat larger.

      Time of year could matter a great deal, affecting whether the ITCZ was north or south of the eruption when it happened, and how much time the sulfate levels had to decay between the eruption and the start of northern hemisphere spring. When was the sulfate veil effect on the quality of sunlight and the sky color first noticed near Basel in connection with this event?

      • Dempo is an interesting one, I think most people just assume Sumatra = Toba + Sinabung but there’s a few calderas littered down the west coast.

        What I would do is, instead of just taking ice cores from the poles, take them from the Urals, the Alps, the Pyrenees, the Tibetan Plateau etc. and triangulate the point of origin of a sulfate spike. I imagine the money isn’t there to do this.

        • I like this idea. Don’t forget glaciers in the Andes and in North America.

          • Glaciers in the Andes, what about this: “The tephra layers were deposited 3,034±621, 2,027±41, 1,557±177, 733±112, and 450±70 a cal BP. The ages of all but the youngest tephra layer overlap with those of known eruptions from Tungurahua.” Andean Geology, Late Holocene tephrostratigraphy from Cajas National Park,southern Ecuador, *Stéphanie H. Arcusa1, Tobias Schneider2, 3, Pablo V. Mosquera4, 5, Hendrik Vogel6, Darrell Kaufman1, Sönke Szidat7 Martin Grosjean3. Enormous time intervals. Quilotea in Siebert’s and Simkin’s volume for 1280 with a questionmark and VEI 6.

            Another interesting event is the 1343 Naples Tsunami possibly caused by a Stromboli flank collapse.

          • @Denaliwatch
            So to clarify/be sure I’m understanding this, the youngest of those tephra layers, the one deposited about 450 +/- 70 years ago, is NOT a layer from Tungurahua, and they don’t know where it comes from?

            There was a really big eruption in 1600, Huaynaputina, that is 420 years ago.

            Intriguing.

      • I don’t mind my candidates being eliminated ;-). Dempo looks very interesting to me, however, because it does look about right.

        As far as bathymetries, google maps seems to be up to date so perhaps someone might check. It would seem however that with a submarine volcano eruption or phreatic eruption of magnitude VEI6 or close to 7, that tidal waves would have occurred too, connected to the eruption.

        My reason for mentioning the Kuril Islands is because there are a lot of calderas in that stretch, I think more than any other place in the world.

        I would like to take a better look at the sulfate levels, as that could possibly distinguish between a north and south hemisphere eruption, and I think Carl mentioned that this eruption has to lie in a zone of 30 – 25 degs north or south of the equator to qualify.

        It is amazing how much we don’t know as the NEEM 2011-S1 data shows from 0 to 1000 CE. almost all unknowns.

  3. Well the Town of Grindarvik has selected two names for the new lava field at Fargradalsfjall; Fagradalshraun and Fagrahraun

    https://www.ruv.is/frett/2021/04/21/fagradalshraun-og-fagrahraun-urdu-fyrir-valinu

    Via giggle translate and my edits

    At a meeting of the town council of Grindavík yesterday, it was decided to refer two proposals for the name of a new lava field at Fagradalsfjall [Fair Valley Mountain] to the Place Names Institute for comment. They are Fagradalshraun [Fair Valley Lava] and Fagrahraun [Fair Lava]. About 340 proposals were received for the name of the new lava in a place name competition that the town of Grindavík held from 31 March to 9 April.
    “The conclusion was that after reviewing the ideas that were received, which were 339, evaluated this and weighed that the lava should be called either Fagradalshraun or Fagrahraun,” says Fannar Jónasson, mayor of Grindavík.

    Dalahraun, Geldingadalshraun and Ísólfshraun also suggested
    He says that these were the proposals that were most often mentioned in the competition. The intention is to also name the craters Fagradalsgígar [Fair VAlley Craters] or Fögrugígar [Fair Craters]. Other ideas that were often mentioned were Dalahraun [Valleys/Dales Lava] , Geldingahraun [Gelding/Wether Lava] and Ísólfshraun [Ísólfur’s Lava], but Geldingahraun already exists in the vicinity. The lava has also flowed in Meradali.

    There is a source that refers to the fact that the settler Ísólfur and the first owner of Ísólfsskáli was buried at a certain place in Geldingadalur, but Minjastofnun [Artifacts Institute] made sure that it was not found at that place before he went under the lava.

    Eggert Sólberg Jónsson, director of the leisure and culture department of Grindavík and an ethnographer, took part in the competition. “The antecedent refers to Fagradalsfjall, which derives its name from the valley west of the mountain, and the antecedent also refers to the Fagradalsfjall system, which is one of the volcanic systems on the Reykjanes peninsula. As for Fagrahraun, the reasoning is the same, but the antecedent also refers to how many people went to the lava to see its beauty, “says Eggert.

    “These were really great proposals, very many and from all over the world in Icelandic and other languages,” says Eggert.

    Kórónuhraun, Ölmuhraun and Góuhraun
    Eggert says that many proposals have reflected the coronary virus epidemic that is clearly on people’s minds, such as Kórónuhraun, Covidhraun and Ölmuhraun. It was also suggested that the craters be named for the trio, Alma Möller, the Director of Health, Þórólfur Guðnason, the Chief Epidemiologist, and Víðir Reynisson, the Chief of Police for Civil Protection, but these proposals were not accepted. Góuhraun was also a popular proposal, which some travelers have probably taken a bite out of after the walk in Geldingadalur.

    The Township is now awaiting for the Place Names Institute to return an opinion on proposals for the two names.

    The place-name tradition is important
    “It is important to keep the place name tradition and preserve the place names,” says Eggert. They are an emotional issue for many. He says that the general public is getting to know place names better and the eruption will hopefully make people better acquainted with the history behind place names in many parts of the country.

      • Well… By laws places cannot be named after living persons, so that needs the question if you are not telling us something about Carl…

    • I’m slightly disappointed. It just seems so… boring and practical. Following the precidents set in perpetuity, when offered a chance to do something a bit more imaginative the Icelanders stick with conventionality. Will we get proper names for the individual craters? Or must I still refer to 3 or 4 sets of names each time to be clear about which vents are being referred to?
      I saw one suggestion of the Xmas elves, with the fissures being named in the correct order. That set of names did appeal to me, rooted as it was in the Icelandic mythtic traditions. And would have preserved the eruption order within the naming sequence.

  4. I was bemused to see this visitor photographing the volcanic delights of Iceland just now:
    .

    • I wonder what is that white spot in the middle of the picture, today in the morning a lot of people are hangin around and they put that over there…they’ve got some ~ground~ activities….

  5. Just logged on for the day and it seems that everything is relatively quiet at Fagradalshraun (I like this name!), although the quakes east of Svartsengi last night and through today are somewhat interesting. Using the Mag 2.0 > filter on the IMO’s website seems to suggest a very vague decrease in depth as the day has progressed.

    An eruption here, while even more accessible to tourists than the current site, could pose a more immediate threat to the Blue Lagoon and Grindavik, if said eruption was long lasting enough. Will be interesting to see how things develop.

    • all that quakes are along an old fissure. as far as i can understand from field picture map….i don;t know…there are recordings about fissure reopenings after a period..long one?

  6. Made a quick painting of the escaped lava, the arrows point to the three ways it can climb out from the bowl, all exits are within the same two heightcurves (10m), so it shouldn’t take too much for it to climb over into Nathagi, though I suspect it will climb back over into Meradalir first, just based on it being the shortest distance horizontally to travel. The numbered location marker is where the two cameras are located (To an accuracy of 4 decimals)

    • Many more big eruptions… Just wait for a really huge deep dike intrusion at Krysuvik, will be called a failed eruption by everyone at first, and then eruptions will happen there yearly for a decade, ramping in scale from tiny to big until theres a mini Laki right outside Reykjavik. It is lucky the topography will take flows away from most of the inhabited areas. Or maybe all of that will happen in a single run, big lava flood right away, turning to a single vent with a lava river and fountain, and someone can call that Eldborg to match all of the other Eldborgs that are in that area 🙂

    • Have they aged the Pleistocene volcanics? As in can they tell if they erupted within years of each other – or is it not that precise?

      Read somewhere that the Pleistocene volcanoes may be waking up.

  7. Comparing the two longest distances the lava has flown, it is quite remarkable how similar the distances are, the Meradalir flow has the edge in distance traveled, but not by many pixels, also it had the advantage of a lot of height difference, though I suspect it has been superseeded now at the time of writing.

  8. To Albert: NO! Never boil coffee… You may boil the water before; but not ever boil the coffee… Boiling Coffee cracks it and makes it bitter. As You were… 😉

  9. I noticed something about the far eastern point of Reykjanes volcanism, it looks like Hengill and Brennisteinsfjoll dont erupt together very easily.

    https://imgur.com/a/7sqo32s

    This is the cycle that happened about 2000 years ago, Hengill last erupted in this cycle creating the lava flow of Nesjahraun and the island of Sandey in Thingvallavatn, eruption was about 0.5 to maybe 1 km3 of lava, quite big for this area. Krysuvik more or less erupted the same as it did in the middle ages, Brennisteinsfjoll though only had at most 3 eruptions and all of small scale.

    https://imgur.com/a/PJPQmLy

    This is the same 3 volcanoes for the Reykjanes Fires, obviously Hengill is completely absent, but Brennisteinsfjoll erupted much more, and much larger in volume overall than it did a millennium earlier.

    Its not to say they actually alternate, Hengill has only erupted in a few other cycles overall in the Holocene, and not regularly, but that if it does show an obvious sign of erupting then Brennisteinsfjoll might stay pretty quiet. It also could work in reverse with a lack of any activity at Brennisteinsfjoll indicating possibly an eruption at Hengill instead.

  10. At 5:43am on the mbl cam: a small part of the left cone broke and a lavariver starts flowing out

  11. Going back to the OP, Basel (I know, late to the party) it’s been a great nostalgic trip for me. Dar Husband and I honeymooned in Switzerland, nearly 39 years ago. We took many more holidays there, in various locations. We always took the train, DH being a Railway Signalling Engineer. Go figure.

    The first time, we travelled by day from Hook of Holland to Brunnen on Lake Lucerne, then moved locations to Spiez, on Lake Thun. Lots of hiking and rack railways and chairlifts and cable cars, with a trip to the Jungfraujoch and Beatusholen, ending with dinner at sunset on a Lake Thun ship. Idyllic.

    Other times, we’d take the night train stumbling off in Interlaken East, sipping hot chocolate and scoffing pains au chololat as cyclists rode past on their second leg of the local triathlon (not for the faint-hearted). Later we would introduce our two offspring to this family tradition.

    We always slid seamlessly through Basel; better, more spectacular prospects filling my eyes, eager for the familiar shapes on the horizon that signalled mountains ahoy!

    Time wound on and the hiking got less, and we ventured southwards to Lake Como (the Hotel at Menaggio is a tale for another time, a real-life Fawlty Towers), stopping off at Basel on the way back to break the fatiguing journey. We wandered around the historic centre, ending up at a restaurant by the bridge over the river. As we ate, a jazz beat combo appeared on a barge in the middle of the river and proceeded to serenade a growing crowd for the rest of the evening, concluding with a grand fireworks display on a second barge.

    Hoping we can get back to globetrotting soon as covid and illness permits. First stop Iceland, of course…

    • Big smile on my face reading your comment. Knowing the area well enough. June is the month to go there.
      Don’t forget Graubünden and the Rhätische Bahn. Let’s blow this freaking covid away!

      • I didn’t recognise the name, but yep, been there, done some of that, haven’t got the tee-shirt though.
        Furkeroberalp, down to the Matterhorn, holiday based in Fiesch. The Aletsch glacier, viewed from the south <3

    • Feeling wistful reading this. I miss international travel … so many trains not yet ridden, breweries not yet visited and volcanoes not yet seen.

      • Have you tried the brewery restaurant at Heidelberg? Ye gods, the portions…

  12. No eqs on the Reykjanes Peninsula since 6am, nearly 4 hours. Something brewing?

    • If you can’t see the volcanoes – it’s raining.

      If you can see the volcanoes – it’s about to rain.

      Albert, who i believe resides in or near Manchester may appreciate where that comes from?

  13. Can’t see a damn thing on any of the three cams today, and for some reason it’s night on the mbl.is one, at what’s supposed to be half past two in the local afternoon!

    Why does this keep happening? I almost never can’t see at least a kilometer from my own windows, so why do these cams seem to struggle to see through any kind of cloudy or rainy day?

    • Heavy rain and mist. It is a cloud forest without the forest bit.

      And in case you wondered, Manchester has a beautiful, sunny, cloudless day. In fact we have had almost no rain so far this month and none predicted before May. We sometimes get these spells of spring weather when high pressure is parked over Ireland

      • Yep – Indeed stunning weather here in Dublin at the moment. Blue Bird skies and a pleasant 14 degrees in the sun. Expected to last at least another week.

        • Aaah, Dublin. Wonderful city, with a collection of gold torcs to die for. And the beautiful Liffy.

      • I’m landscaping my garden (the second glorious month of shifting dirt), with about 8 weeks to go on the project.
        The dry weather can just keep right on going as far as I’m concerned… The sooner to be finished !

      • Cloud forests are found at altitude. This is a few hundred meters above sea level.

        • This is Iceland. What the hills lack in elevation, the clouds make up by their lack of elevation. They have the entire north atlantic ocean to prepare. When the weather hits Iceland, it really goes for it. The low temperature limits the amount of precipitation, but clouds form very easily. A small rise in the land elevation is sufficient for the temperature to drop to the dew point

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