GeoLog

mexico

Geosciences Column: How climate change put a damper on the Maya civilisation

Geosciences Column: How climate change put a damper on the Maya civilisation

More than 4,000 years ago, when the Great Pyramid of Giza and Stonehenge were being built, the Maya civilisation emerged in Central America. The indigenous group prospered for thousands of years until its fall in the 13th century (potentially due to severe drought). However, thousands of years before this collapse, severely soggy conditions lasting for many centuries likely inhibited the civilisation’s development, according to a recent study published in EGU’s open access journal Climate of the Past.

During their most productive era, often referred to as the Classic period (300-800 CE), Maya communities had established a complex civilisation, with a network of highly populated cities, large-scale infrastructure, a thriving agricultural system and an advanced understanding in mathematics and astronomy. However, in their early days, dating back to at least 2600 BCE, the Maya people were largely mobile hunter-gatherers, hunting, fishing and foraging across the lowlands.

Around 1000 BCE, some Maya communities had started to transition away from their nomadic lifestyles, and instead were moving towards establishing more sedentary societies, building small villages and relying more heavily on cultivating crops for their sustenance. However, experts suggest that agricultural practices didn’t gain momentum until 400 BCE, raising the question as to why Maya development was delayed for so many centuries.

By analysing two new palaeo-precipitation records, Kees Nooren, lead author of the study and a researcher at Utrecht University in the Netherlands, and his colleagues were able to gain insight into the environmental conditions during this pivotal time, and the impact that climate change could have had on the Maya society.

To determine the regional climate conditions during this period of time, the authors examined a beach ridge plain in the Mexican state of Tabasco, off the Gulf of Mexico, which contains a long-term record of ridge elevation changes for much of the late Holocene. Since precipitation has a large influence on the elevation of this beach ridge, this record is a good indicator of how much rainfall and flooding may have occurred during Maya settlement.

A large part of the central Maya lowlands (outlined with a black dashed line) is drained by the Usumacinta (Us.) River (a). During the Pre-Classic period this river was the main supplier of sand contributing to the formation of the extensive beach ridge plain at the Gulf of Mexico coast (b). Periods of low rainfall result in low river discharges and are associated with relatively elevated beach ridges. Taken from Nooren, K et al., 2018

Additionally, the researchers also assessed core samples taken from Lake Tuspan, a shallow body of water in northern Guatemala that is situated within the Central Maya Lowlands. Because the lake receives its water almost exclusively from a small section of the region (770 square kilometres), its sediment layers provide a good record of rainfall on a very local scale.

The image on p. 74 of the Dresden Codex depicts a torrential downpour probably associated with a destructive flood (Thompson, 1972). Taken from Nooren, K et al., 2018

The research team’s analysis suggested that, starting around 1000-850 BCE, the region shifted from a relatively dry climate, to a wetter environment. Such conditions would have made a farming in this region more difficult and less appealing compared to foraging and hunting. The researchers suggest that this change in climate could be one of the reasons why Maya agricultural development was at a standstill for such a long time.

The researchers also propose that this long-term climate trend could have been brought on by a shift of the Intertropical Convergence Zone (ITCZ), a region near the equator where northeast and southeast winds intermingle and where most of the Earth’s rain makes landfall. The position of this zone can move naturally in response to Earth’s changes in insolation, and a northerly shift of the ITCZ could help account for some of the morphological changes the authors observed in the precipitation records.

After more than 450 years of excessive rainfall and large floods, the records then suggest that the region experienced drier conditions once again. By this time period, the Maya populations began to rapidly intensify their farming efforts and develop major cities, further suggesting that the wet conditions may have helped delay such efforts.

This is not the first time the Nooren and his colleagues have found evidence of major environmental influence on the Maya civilisation. For example, earlier research led by Nooren suggests that, in the 6th century, the El Chichón volcano in southern Mexico released massive amounts of sulfur into the stratosphere, triggering global climate change that likely contributed to a ‘dark age’ in Maya history for several decades. During this time, often referred to as the “Maya Hiatus,’ Maya societies experienced stagnation, increased warfare and political unrest. The research results were presented at the 2016 General Assembly and later published in Geology.

The results of these studies highlight how changes in our climate have greatly influenced communities and at times even shaped the course of societal history, both for better and for worse.

By Olivia Trani, EGU Communications Officer

References

Ebert, C. et al.: Regional response to drought during the formation and decline of Preclassic Maya societies. Quaternary Science Reviews 173:211-235, 2017

Nooren, K., Hoek, W. Z., Dermody, B. J., Galop, D., Metcalfe, S., Islebe, G., and Middelkoop, H.: Climate impact on the development of Pre-Classic Maya civilization. Clim. Past, 14, 1253-1273, 2018

Nooren, K.: Holocene evolution of the Tabasco delta – Mexico : impact of climate, volcanism and humans. Utrecht University Repository (Dissertation). 2017

Nooren, K. et al.: Explosive eruption of El Chichón volcano (Mexico) disrupted 6th century Maya civilization and contributed to global cooling, Geology, 45, 175-178, 2016

Press conference: Volcanoes, climate changes and droughts: civilisational resilience and collapse. European Geosciences Union General Assembly 2016

Caltech Climate Dynamics Group, Why does the ITCZ shift and how? 2016

Mexico earthquakes: What we know so far

Mexico earthquakes: What we know so far

On Friday 8 September 2017 at 04:49 am UTC, a magnitude 8.1 earthquake hit off the coast of Mexico, 87 km SW of Pijijiapan. According to the U.S. Geological Survey, the epicentre was at 15.07 N, 93.72 W at a depth of about 69.7 km. Yesterday, another strong (magnitude 7.1) earthquake hit central Mexico, 55 km SSW of the city of Puebla and 120 km south of Mexico City.

Despite the lower magnitude, yesterday’s earthquake, which struck at a depth of 51 km, has caused widespread destruction. At the time of writing, official estimates put the death toll at 217 (according to Mexico’s National Coordinator for Civil Protection, Luis Felipe Puente), with shaking causing damage to and the collapse of hundreds of buildings in Mexico City and surrounding areas.

“The M 7.1 earthquake was much closer to Mexico City, a city build on a dried lake bed; this caused presumably (needs to be confirmed by data) much higher shaking in the densely populated capital then the larger, but farther M 8.1 event,” explains Martin Mai, President of the EGU’s Seismology Division.

“Both earthquakes were intraplate normal faulting events, not occurring on the interface between the subducting and overriding plates but rather inside the subducting plate,” adds Vala Hjorleifsdottir, a researcher at the National Autonomous University of Mexico.

These intraplate earthquakes generate relatively strong and rapid shaking, compared to their counterparts breaking the plate interface.  Furthermore, as the waves are generated deeper in the Earth, they do not travel through shallower material that damp them as they travel, and they are still strong when they arrive to the City of Mexico and neighbouring areas.  For these reasons, combined with their proximity to populated areas, these events can be more destructive than expected by their magnitude.

The U.S. Geological Survey estimated that significant causalities are likely in the region. Given the mix of vulnerable and earthquake resistant structures, the economic loss is also expected to be high. For more information visit impact pages of the event on the USGS website.

Six days after the latest earthquake, rescue workers are still search for victims among the rubble. This visual of Mexico City gives an impression of the scale of the devastation in the country’s capital city.

“Mexico City [is] built on a dried-out lake bed, or on ‘landfill’ of unconsolidated sediments.  The interaction between the incoming seismic waves and the sediments cause the waves to amplify and the duration of shaking to increase.  Both of these factors are devastating to buildings,” explains Hjorleifsdottir.

As to whether the two earthquakes are linked, scientists are fairly certain that the normal mechanisms which are known to trigger an earthquake after another didn’t come into play for the M 8.1 and the later M 7.1. At more than 600 km between the two quakes, they occurred, too far from one another. In addition, if shaking from an early earthquake is going to trigger a second, it is expected to happen shortly after the initial tremor, not 12 days later.

However, there are other mechanisms, which are less well understood, for example the triggering of earthquakes in hydrothermal areas and volcanoes, over large distances, for a period after large events.

“We believe this has to do with the behaviour of fluids in these areas, that promote the occurrence of earthquakes in these regions.  More research is needed to tell whether any of these other methods caused triggering of the second event,” says Hjorleifsdottir. Mai also adds: “It could be that stress changes caused by the M 8.1 event brought the fault (system) on which the M 7.1 earthquake happened closer to failure; but this requires detailed quantitative analysis”.

Editor’s note: Last updated 02.10.2017. This post will be update as more information about the earthquake becomes available.

With thanks to Martin Mai (EGU Seismology Division President), Vala Hjorleifsdottir, Paco Sánchez and Marco Calo (National Autonomous University of Mexico).

Further reading and resources:

U.S. Geological Survey overview of 19.09.2017 M 7.1 earthquake (includes interactive, shake and regional information maps)

U.S. Geological Survey overview of 08/09.2017 M 8.1 earthquake (includes interactive, shake and regional information maps, as well as finite fault results and moment tensor information)

Temblor blog post on M 7.1 earthquake

Temblor blog post on M 8.1 earthquake

Did Mexico dodge a bullet in last week’s M=8.1 earthquake? (Temblor blog post on dynamics of 8th September quake)

European-Mediterranean Seismological Centre information about yesterday’s earthquake

SSN (Mexico) page about yesterday’s earthquake (in Spanish)

GFZ GEOFON Global Seismic Network event page for yesterday’s earthquake

Mexico City, Before and After the Earthquake (New York Times visualisation)

Are Mexico’s two major earthquakes related, and what could happen next? (Temblor blog)

Shocked and shaken to the ground: An eyewitness report from Mexico City (Temblor blog)

Mexican Earthquakes: Chain Reaction or Coincidence? (Temblor blog)