What happens to the boats? The 1755 Lisbon earthquake and Portuguese tsunami literacy Open Access

During the twentieth century earthquakes killed almost two million people. The ones responsible for most of the deaths and destruction are those of high magnitude and have a broad distribution around the world. Table 1 shows the earthquakes that caused the highest number of deaths, by country, during the twentieth century.

Despite the related death toll, the level of destruction, and their wide distribution around the world, the frequency of earthquakes of great magnitude is measured on a scale of hundreds of years, and thus the collective memory of them seems to fade away. This assertion may seem contradictory, given that the Lisbon earthquake, which occurred on 1 November 1755, appears to be an event that is still well known by many Portuguese. This may result from the peculiar characteristics of the event, the great magnitude of the earthquake, the tsunami and fire that followed, and the irreplaceable destruction of symbolic places of historical and spiritual value (Vasconcelos et al., 2014). Spurred by the event, a vast amount of literature was produced in areas applied to seismology and disaster mitigation, ranging from theology and philosophy, to art, literature, and eighteenth century studies, and urban planning (Chester, 2001). The Lisbon earthquake of 1755 is probably the greatest seismic disaster to have struck western Europe: it affected an area of ∼800,000 km² and killed as many as 100,000 people, 1000 of which lived in the Algarve, in the south of Portugal (Chester and Chester, 2010).

For many years scholars have tried to comprehend every imaginable indicator to determine when the ground would crack; for example, they looked at animal behavior, gas leakage, radio signals generated by rock, and the level of the water in wells (Redfern, 1991). The seismologist’s capability to foresee earthquake disasters and the extent of destruction immediately after an event has greatly increased during the past decade (Lambert and Oberhaensli, 2014; Wyss, 2015). However, this scientific progress is not being used by governments to prepare and reduce seismic risk, or by the mass media reporting on disasters. For example, physical evidence is an important approach for educating local people about large paleotsunamis that have inundated their towns in the past (Goto et al., 2014). The fact is that we could do better than we are doing now with regard to protecting the population and reducing earthquake risk, especially by preparing the youngest for these types of devastating events. The history of science is intrinsically useful and should be made familiar to all students by including historical items in science programs (Matthews, 2015).

In the eighteenth century, Lisbon was one of the largest cities in Europe, with an estimated population of 275,000. On 1 November 1755, Portugal witnessed the biggest catastrophe that had ever occurred in the country. The 1755 Lisbon earthquake was one of the most powerful in history, with a Richter magnitude estimated between 8.6 and 9.0 (Rodrigues and Russel, 2008). According to Amador (2007), earthquakes are probably the natural phenomena that have had the biggest impact on, and repercussion through, the history of humanity, both at the scientific and philosophical levels. The 1755 Lisbon earthquake had such an impact that the intellectual experts of the time described and illustrated the phenomenon exhaustively, in Portugal and all over the world. Some records of the time are well preserved, and have been studied in order to better understand the catastrophe. One of the most faithful descriptions of the earthquake can be found in Sousa (1928, p. 479), quoting Moreira de Mendonça: “Shortly after nine-thirty a.m. with the Barometer at 27 inches and seven lines, and the thermometer of Reaumur at 14 degrees above the ice, with a light wind blowing from Northeast, the land started to shake with a pulsation from the center to the surface, and as the impulse increased, it continued to shake forming a balance from the North to the South… .”

It is known that the earthquake occurred at 09:40 a.m., on a calm day with a temperature of 14 °C and a weak northeast wind. It occurred in three distinct phases: the first phase, which lasted for 1.5 m, was not very violent; the second phase, a slower one, caused serious damage; the third phase lasted close to 3 m and was the most violent of all, being responsible for the greatest number human losses and material damage (Fundação Luso-Americana, 2005). The “formidable earthquake” (Sousa, 1919, p. 88) happened on All Saints Day, a day extremely important to the Portuguese. Being mostly Catholic, the majority of the population was at church at the time of the event, and the violence was felt and heard in a thundering way that was quickly associated with a holy punishment; it was a moment of panic (Carvalho, 2006).

The epicenter of the 1755 earthquake must have occurred in the Azores-Gibraltar fault, next to the bank of Gorringe. However, the very high magnitude of the earthquake cannot be explained by a simple disruption along the plate, south of that bank. More recent studies, developed by geologists in the area, suggest a possible zone of subduction in the transition of a passive to an active edge (Duarte et al., 2013). The plate is splitting in two and is starting subduction. The major intensity of the earthquake was felt in Lisbon and in southern Algarve (Fig. 1). However, it was what followed that caused the highest number of victims. On the one hand, fires lasted for more than six days in the downtown of Lisbon, fed by the materials that were used in the buildings. As described by Morganti (1755, p. 4), “The so voracious fire that ended up by ruining the best part of the City, which began in the same hour.” On the other hand, a tsunami hit Lisbon at 11 a.m., and was described by Moreira de Mendonça: “To these impulses of the land the sea removed, allowing the vision of its bottom in its edges as never seen before, and raising these in towering mountains, will shortly after spread over all the maritime villages with such an impetus, that it seemed to intend to sink them by extending its limits… .” (Sousa, 1928, p. 480–949).

The people, who in panic had started to run away from the churches, moved toward the river, to a zone farther away from the terrible destructive scene they were witnessing. However, it was this very act that unwittingly led them to the tsunami that had just hit a wharf on the Tejo River. This tsunami was responsible for a huge loss of life and threatened not only those living in Lisbon, but also those along the coastal regions throughout southern and western Iberia and the Maghreb region of North Africa (Chester, 2001).

A tsunami is usually associated with earthquakes, landslides, or volcanic eruptions in, or adjacent to, oceans. It results in sudden movement of a water column in which the circulation comes from the surface to the bottom of the sea, which makes its speed related to the depth. As the wave comes close to land it reaches shallower waters and diminishes.

In 1755, the wave must have been ∼15 m high; it extended 500 m into Lisbon, and flooded downtown. The tsunami hit not only the Portuguese coast, including the Algarve (extended 30 m into Algarve), but also the southwest of Spain, northern Africa, the British Isles and the Netherlands (Fundação Luso-Americana, 2005).

After the almost complete destruction of downtown Lisbon, the urgent reconstruction of the city became a priority.

Times of crisis are often opportunities for reforms and the reorganization of societies. The 1755 Lisbon earthquake and the tsunami that followed were no exceptions. For the first time, a western government organized a large-scale coordinated emergency response to a disaster (Mendes-Victor et al., 2009). Following the earthquake, Marquês de Pombal (Secretary of the State for the Internal Affairs of the kingdom of D. José I), immediately sent troops to the Algarve in order to keep law and order and to prevent north African corsairs from exploiting the situation. These law enforcement police forces were the first example in the world of a state taking the responsibility for a coordinated and centralized response following an earthquake (Chester and Chester, 2010). After securing law and order, Marquês de Pombal sought a scientific hypothesis for the origin of this tremendous event. Being very forward thinking for his time, he then distributed a scientific inquiry to the parish priests in order to investigate the facts that could explain the event (Table 2).

The survey, of “purely seismological nature,” had 13 questions about the meaning and characteristics of the shock, and the damage that it had inflicted. The survey was distributed to the parish priests in Lisbon, Lagos, and Faro (the latter two in the region of Algarve). Out of respect for Marquês de Pombal, the priests answered the survey promptly and with accuracy (Carneiro and Mota, 2007). The earthquake destroyed about two-thirds of the streets in Lisbon, 17,000 homes, 35 churches, 64 convents, all the hospitals, and 33 manorial houses (Quadros, 1989). Sousa (1919) determined that those constructions built on limestone with rudists, in basalt or basaltic tuft, and on the thick banks of calcareous molasse and of Paleogene–Neogene sandstone, in general, had resisted the earthquake; he also learned that the constructions built on strong Paleogene–Neogene clay banks had equally resisted, in general, the seismic shock. Sousa (1919) found that the constructions that were on and sands and mudslides, in general, were destroyed or almost destroyed. The fragility of the construction of the time focused the destruction and the fires in the city after the earthquake.

Portugal received aid from countries such as Brazil, England, and Germany that offered financial help and construction materials. Laws were also passed charging emergency taxes and forbidding construction in the city. There was resolute concern to understand the event and to try to prevent another of the kind. Marquês de Pombal considered it to be a priority to take the debris out of the streets, drain stagnant waters, demarcate the destroyed areas, and assess and measure the squares, streets, houses, and public buildings that had been destroyed; he was envisioning the future of Lisbon. Thus, Marquês de Pombal asked Manoel da Maya, the very meticulous high-engineer of the kingdom, to present an integrated urban plan for the birth of a new city that was innovative and included the seismic engineering concerns and knowledge of the time.

On 6 November 1755, five days after the earthquake, Manoel da Maya reported the damages that the Portuguese national archive, Torre do Tombo, had suffered; he urged the government to safeguard books and documents, and asked permission to build a wooden shed in the gun square of Saint George Castle to store all the documents that had survived the earthquake and that were spread throughout the city (Rodrigues and Russel, 2008). Manoel da Maya argued that this would allow these documents to be protected against robbery and would keep them out of the rain. However, Manoel da Maya did not work alone; he was surrounded by personalities in engineering and architecture, such as Eugénio Dos Santos and Carlos Mardel. In a report of the 1755 Lisbon Earthquake (Ayres, 1910, p. 20): “When, from the ruins of this horrible earthquake, the energetic will of Marquês de Pombal built, lined up, colourful and beautiful, the new city, the military engineers were the major auxiliaries of that iron will. The chief engineer Manoel da Maia and his officers had directed and executed the major work.”

The report written by Manoel da Maya (1756), aged 79 at the time, presented several proposals for the reconstruction of Lisbon and demonstrated the great interest that he devoted to this subject (Quadros, 1989). In the first part of the report, point 1, Manoel da Maya (1756, p. 2) wrote, “Found and observed the destruction of the city of Lisbon we must begin its renewal, and as it can be done in different ways, it seems also necessary to choose the one that has more advantages and less drawbacks.”

On 4 December 1755 Manoel da Maya sent the report, to the Duke of Lafões, and Marquês de Pombal received and studied it. The chief engineer divided the report, into three parts, presenting different hypotheses for the reconstruction of Lisbon, architectural models, and observations of practical and technical nature. The plans were divided between those that proposed a renovation of the city with new buildings but keeping the same urban planning, and those that proposed a whole new Lisbon with a better urban planning. The six plans that were developed were analyzed by Marquês do Pombal, who chose plan 5, proposed by Eugénio dos Santos. This plan presented a new Lisbon, and consisted of a rather complex web of streets that linked the entire downtown. The square shape of Terreiro do Paço (where the palace of the king was located for about two centuries) was defined and three streets went up to the Rossio (the liveliest square of Lisbon). Three other streets began three blocks above Terreiro do Paço to the south line of Rossio. The crossing streets, seven in all, together with the remaining ones, contributed to a very dynamic mesh in the Lisbon area. The variations of the widths of the streets and the shapes and orientations of the blocks contributed to the dynamics. We can read from the descriptions of Manoel da Maya (and the Portuguese military engineers) of the 1755 earthquake that: “To these observations of the illustrious writer we will add that, if that scientific principle was actually followed, you can not deny the great Pombal the glory of this superior way in which his work was performed; but it is also fair to recognize that the engineers who performed such a work knew and could put into practice that important precept” (Ayres, 1910, p. 6).

Some innovations were introduced at the time, such as the gaiola pombalina (pombaline cage), where wooden stake foundations were used and tests were performed to simulate the effects that earth movements caused (Almeida, 2005). The word “gaiola” (cage) refers to a wooden structure that, because of its elasticity, adapts to the movements of the soil when shaken by an earthquake, either resisting it and standing up, or drawing attention to the masonry that could collapse (França, 1981, p. 103). The construction of this structure began when the foundations of the walls reached the level of the ground outside or, in most cases, from the masonry structure of the ground floor (França, 1981, p. 103). Foreigners reported that the Portuguese claimed that houses built this way specifically resisted the earthquakes that often occurred in Lisbon. Furthermore, in an attempt to prevent the collapse of buildings, arcs were built so as to better transmit the loads to the ground, and wooden stake foundations were laid, allowing stability in an unstable ground, as was the case of the Lisbon downtown. Pine stakes, used as foundations, were ∼1.5 m long and 15 cm in diameter. The Pombaline Cage referred to herein as a brilliant tool for lessening the impacts of earthquakes, also served to test and assess the effects of earthquakes of different magnitudes. Under Carlos Mardel’s command, the army marched over the Pombaline buildings, and tested them against strong vibrations. However, history can be interpreted differently, considering that Marquês de Pombal was a Freemason and that plan 5, which he chose, included Masonic symbols and was developed by Eugénio dos Santos, also a Freemason. According to this line of thought, after the 1755 great tragedy, Lisbon was rebuilt as a huge temple of Freemasonry. Whatever the case, the innovation, the seismologic concerns, and the intelligent choices of the plan for the reconstruction of Lisbon, made this city “…the first of the modern cities and the last of the ancient cities…” (França, 1981, p. 103).

In order to evaluate Portuguese citizens’ scientific literacy about tsunamis, a survey was done, including 206 structured interviews. The results were qualitatively and quantitatively analyzed.

Interview scripts were designed by three members of the research team, over three stages, and were validated by two professionals in geoscience education and one geology professional. In order to assess Portuguese citizens’ knowledge about tsunamis, three main issues were addressed: (1) understanding tsunamis and their consequences based on a hypothetical scenario; (2) historical knowledge about tsunamis that occurred in the country; and (3) relevance of including themes related to tsunami relief and prevention in the geosciences programs of elementary and middle schools.

The interview starts by showing a previously drawn scenario (Fig. 2) representing a tsunami epicenter and showing three boats placed in different places of the ocean. Respondents were asked to think about the situation and to answer question 1, “Regarding this scenario, which boat do you think will suffer the most after the release of energy?”

Question two (in two parts) assessed the respondent’s knowledge concerning historical tsunamis: “Do you know any earthquake that has caused a tsunami in Portugal? If so, when did it happen and where was it more intensely felt?”

Question three (in two parts) asked for the interviewee’s opinion regarding the importance of this subject in Portuguese geoscience programs: “Studies suggest that another tsunami, like the one that occurred in 1755 in Portugal, may occur again. Do you consider it important to include themes regarding seismic risk and civil protection mechanisms in the geosciences programs at elementary and middle schools level?”

At the end of the interview, the correct answer to question one was explained by showing the participants Figure 3.

An effort was made to keep the interview moderately brief, so as to prevent respondents from not completing it. Thus, in addition to the previously mentioned questions, only data related to gender and age were collected. We chose an intentional sample (i.e., selected for specific prescribed criteria) as described in the following.

After the validation of the interview script, two members of the research team conducted the interviews. Portuguese citizens were asked to participate in a public space (the citizens’ bureau, a place where people go, for example, to pay water taxes and electricity bills and apply for passports) located in an urban area in a city in the north of Portugal. Portugal is ranked in a United Nations Human Development Report (United Nations, 2015, p. 67) as having a “very high index of human development.”

The interviews were audiotaped for more reliable transcription. Content analysis was subsequently performed with the help of the QSR NVivo 10 qualitative data analysis software package. Two members of the research team independently performed content analysis and subsequently compared their analysis, until a consensus was reached. Some nonparametric tests were done with the help of Softonic SPSS statistics software, version 25 (https://en.softonic.com/s/spss-25).

The study used an intentional sample (i.e., selected for specific prescribed criteria), to which researchers ascribe great potential in terms of representation (of the population) and, simultaneously, to which individuals are expected to be more willing to respond (Vicente et al., 2001). Thus, a busy public space was chosen (in front of the citizens’ bureau) that allowed easy contact with possible respondents, and numerous alternatives if some citizens were unwilling to participate. The interviews took place during the operating hours of the citizens’ bureau (08:30 a.m. until 06:30 p.m.), throughout four days. The sample comprised 107 females (51.9%) and 99 males (48.1%) with ages ranging from 12 to 85 (Table 3). Group 1 (G1) comprised school-age individuals, including those still enrolled in higher education, i.e., postgraduation degrees; group 2 (G2) included individuals present in the labor market; and group 3 (G3) comprised individuals that have reached retirement age. The following analysis takes these groups into account.

Concerning the first question, 42.7% of respondents gave a correct answer (Table 4), designating boat 3 as the one that would suffer the most with the energy release. In spite of this considerable percentage of correct answers, an equally high percentage of respondents (43.4%) chose boat 1, and 13.6% of respondents chose boat 2. More than 50% of the respondents did not know the correct answer.

In analyzing the results presented in Table 4, no relevant differences were found between female and male answers. The performance of an independent chi-square (χ²) test between the genders allowed us to conclude that there is no statistical evidence to claim that age influenced the answers [χ²₍₂₎ = 0.195; p = 0.675], thus indicating that gender does not seem to influence the Portuguese knowledge concerning tsunamis.

When it comes to the age group, no substantial differences were found. The independent χ² test between the three groups (G1, G2, G3) allowed us to conclude that there is no statistical evidence that age influences the answers [χ²₍₁₎ = 0.023; p = 1.000]. Nevertheless, respondents aged from 30 to 39 and from 80 to 89 gave a higher number of correct answers (Table 5). Results reveal a lack of knowledge concerning the tsunami phenomenon and its consequences, and highlight the relevance of increasing Portuguese scientific literacy on these issues.

The majority of respondents (89.8%) did not justify the answer they gave to question 1, although a few explanations were put forward. Only 11 of the respondents who selected boat 1 (13.4%), 2 of the respondents who selected boat 2 (7.1%), and 8 of the respondents who selected boat 3 (10.0%), justified their answer.

For example, 90.9% of respondents who justified the selection of boat 1 referred to its proximity to the epicenter: “So, the boat that is closer to epicenter… the boat 1” (R91).

The respondents who justified the selection of boat 2 presented two main reasons: (1) “The wave must be bigger in position two” (R167) and (2) “This boat picks up the strength of the wave” (R38).

To justify the selection of boat 3, the main justifications given were related to its proximity to the seashore and to the increase of energy and/or wave intensity: “It is the one that is closer to the seashore, boat 3” (R56), and “It is boat 3. Waves intensity increases…” (R158).

Regarding question 2, the majority of respondents (60.2%) did not reveal any knowledge about the tsunami that hit the Portuguese coast (Table 6). In fact, only 19.4% of the respondents knew where and when the tsunami had occurred. Two of the answers that were given are: “In Portugal, only the one that we heard about in Lisbon, in 1755…” (R12), and “In Lisbon. 1755. In the time of Marquês de Pombal” (R162).

As shown in Table 6, no substantial differences were found between genders because the independent nonparametric test gave no evidence of that [χ²₍₁₎ = 0.001; p = 1.000]. However, it seems that citizens aged between 70 and 89 have a better knowledge regarding historical tsunamis that reached Portuguese coast: 50% of them answered this question correctly (Table 7). However, <23% of Portuguese citizens aged between 10 and 69 showed knowledge regarding this historical event that hit their own country.

Citizens aged between 70 and 89 possess a considerably greater historical knowledge, which could result from changes that have occurred in the Portuguese geoscience programs, were it not for the low level of literacy of the Portuguese between 70 and 89 years of age. In fact, the tsunami of 1755 is not currently being explored in the Portuguese syllabus, although it is sometimes referred as an historical example, although no substantial educational and scientifically exploration of this issue is made by teachers. Nevertheless, the independent χ² test revealed no significance between the three age groups and knowing the correct answer versus not knowing or other responses [χ²₍₁₎ = 4.233; p = 0.116].

Concerning the last question, the majority of the respondents considered the inclusion of topics related to tsunami relief and prevention in the geosciences programs to be fundamental. In fact, only 3 respondents (1.4%) considered that there was no need to include those topics in geosciences programs, as shown in Table 8.

Although the majority of respondents considered it fundamental to include topics related to tsunami relief and prevention in geosciences programs (79.9%), they did not provide a solid justification for their opinion. Nonetheless, two main justifications were indicated: (1) to know how to act and to be aware; and (2) to have more information: “I think it is important, as it is necessary to warn our youngsters. They should understand the risks associated to it and how to act in these situations from an early age” (R176); and “Yes, yes. It is suitable, it is suitable for them to be informed” (R42).

Regarding the respondents that did not consider it fundamental to include those topics in geosciences programs, one of them did not justify his answer, and the other two expressed the following: “No, no. Because I think that the risk of it happening is too small. We cannot change the entire curriculum of a child because of a small risk” (R46), and “In the elementary and secondary school, children should be taught the multiplication table, how to read and write. This is what I think it is important to teach. Because nowadays, pre-university students do not know the answer of some multiplications, as 8 × 7 or 7 × 7, for example” (R42).

Following the data analysis it is clear that although the majority of the participants recognize the need to know about these issues, there is a lack of knowledge regarding tsunamis, especially related to the historical tsunamis that reached the Portuguese coast.

The 1 November 1755 Lisbon earthquake violently hit a great part of the Portuguese territory and a vast neighboring geographic zone. It also deeply shook the philosophical thoughts of the time and increased fears and apprehensions among Europeans. The damage was enormous. In order to increase postearthquake assessment, efficiency, and safety, it was decided that a permanent staff should be assigned to, and trained to act on, those kinds of emergencies. Moreover, the existing training program for public servants should be improved and extended to professionals (Azevedo et al., 2009).

The results of this research show that a better knowledge regarding seismic risks is still needed; it should be taught in schools and therefore included in textbooks and geoscience program guidelines, at least in all countries with an eminent tectonic risk (for example, those referred to in Table 1). In general terms, it seems that neither gender nor age influenced the answers to the interview; nevertheless, the eldest respondents seem to know more regarding this historic earthquake, possibly not due to being taught in school, but rather because of stories passed on through generations about the earthquake and the tsunami. As the majority of answers in all respondents were wrong, even these stories are fading away. For Portuguese citizens to be informed, for them to know how to be aware and how to behave in a similar disaster scenario, it is necessary to increase their literacy on this issue. The fact that scientists understand the risk only increases the responsibility of informing both the population and the policy decision makers; the latter, in particular, have the responsibility of informing the public, promoting adequate urban planning, and passing informed related legislation (Lambert and Oberhaensli, 2014). One possibility to increase citizens’ literacy is to include these historical episodes in textbooks, embedding this theme within geoscience programs. As many argue, the inclusion of science history in science teaching is a way to teach students scientific conceptual knowledge and to make them more aware of scientific problems (Matthews, 2015) such as natural risks and hazards. According to the U.S. National Research Council (2010), an inquiry-based approach to the discussion of historical events will ensure that students reflect on and are involved in finding ways to better prevent such damage; in addition, students will discuss ways to reduce the risks of future calamities that may result from tsunamis. If we want citizens to be active and to play a responsible role in the development of their own society, these historical socioscientific issues must be clearly and decisively addressed in the classroom.

This research was carried out within the scope of the Research Project FCT-Pest-OE/CTE/UI0039/2014, funded by FCT (Fundação para a Ciência e a Tecnologia, Portugal). The authors thank reviewer Chris King, an anonymous reviewer, and Guest Associate Editor Suzanne O’Connell for their comments on the manuscript.