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article imageBlue Hole of Belize may explain demise of Mayan civilization

By Stephen Morgan     Dec 28, 2014 in Environment
The mystery of the demise of the 3,000 year old Mayan civilization has baffled historians and archaeologists for decades. However, new research at the Blue Hole of Belize lends weight to the idea that catastrophic drought brought the empire to its knees.
The mighty Mayan culture, which began around 2,000 BC and continued until 800 to 900 AD was one of the most advanced civilizations in the world during its height. Its great pyramids, architecture, urban structures, agriculture, knowledge of astronomy, mathematics, advanced hieroglyphic writing and its famous calender matched many of the achievements of the other great civilizations of antiquity in Egypt, Greece, Mesopotamia, the Indus valley and China.
The Mayan civilization, which encompassed some 19 million people, reached its peak between 300 AD and 700 AD. Its influence was evident over 1,000 km from its central regions and stretched as far as Honduras, Belize, Guatemala, El Salvador and to central Mexico.
This observatory was used  among other things  to predict solar eclipses.
This observatory was used, among other things, to predict solar eclipses.
However, after 700 AD it began a gradual descent into decay and disorder. Why such an advanced society should disappear has given rise to many theories from alien invasion to religious fanaticism and ecological disaster. Definitive proof of the cause has, however, remained elusive.
Now, a study of minerals in the lagoons of Belize's famous Blue Hole confirms that two catastrophic and prolonged droughts lasting over a hundred years most likely led to the disintegration of the Mayan civilization.
Following the first drought, probably between 800 AD and 1,000 AD, the Mayans emigrated north, only to be hit again by another prolonged drought during the Little Ice Age between 1,000 AD and 1,100 AD. That proved to be the terminal blow, coinciding with the fall of the famous city of Chichen Itza.
The theory that drought was the decisive factor in Mayan decline isn't new. Back in 2012, an analysis of a 2,000-year-old stalagmite from the south of Belize pointed to the fact that major reductions in rainfall overlapped with the demise of the Mayan culture. However, this information came from just one area and was therefore insufficient to explain what happened throughout the entire region.
But scientists have recently broadened that research by drilling holes in the sediments in the Blue Hole underwater cave and around the Lighthouse lagoon and the Rhomboid reef, which are surrounded by thick walls of coral. Live Science explains that
"During storms or wetter periods, excess water runs off from rivers and streams, overtops the retaining walls, and is deposited in a thin layer at the top of the lagoon. From there, all the sediments from these streams settle to the bottom of the lagoon, piling on top of each other and leaving a chronological record of the historical climate."
The study's co-author André Droxler, an Earth scientist at Rice University, said, "It's like a big bucket. It's a sediment trap,"
The researchers then analyzed the the ratio of titanium to aluminum in the cores. Rainfall erodes the volcanic rocks in the area, which contain titanium. Low ratios of titanium to aluminum correspond to periods with less rainfall and, on that basis, they calculated that between 800 and 1000 AD, there were only one or two tropical cyclones every 20 years, instead of the normal five or six.
"The main driver of this drought" says Live Science "is thought to have been a shift in the intertropical convergence zone (ITCZ), a weather system that generally dumps water on tropical regions of the world while drying out the subtropics. During summers, the ITCZ pelts the Yucatan peninsula with rain, but the system travels farther south in the winter." Therefore, "many scientists have suggested that during the Mayan decline, this monsoon system may have missed the Yucatan peninsula altogether."
There has been speculation on other factors that could either have arisen from or contributed to the decline. The Mayans, for example, attempted to expand croplands and this led to large scale deforestation, which worsened the drought.
In relation to some earlier research on the same question, the Smithsonian pointed out that, "because cleared land absorbs less solar radiation, less water evaporates from its surface, making clouds and rainfall more scarce. As a result, the rapid deforestation exacerbated an already severe drought."
"In a time of unprecedented population density," it continues, "this combination of factors was likely catastrophic. Crops failed, especially because the droughts occurred disproportionately during the summer growing season. Coincidentally, trade shifted from overland routes, which crossed the heart of the lowland, to sea-based voyages, moving around the perimeter of the peninsula."
Faced with these problems, the local farmers were forced to leave the barren lowlands. Since the surrounding areas could no longer support the urban population, they, in turn, had to evacuate the cities leaving them as the ruins we see today.
These economic problems would have undermined the ruling elite, who depended on agricultural surpluses and profits from trade for their power. This probably led to social unrest and internal disintegration. "When you have major droughts, you start to get famines and unrest," Droxler said.
Even so, forms of the Mayan culture managed to continue as city states in northern Yucatán for a few centuries and their fierce resistance to the conquistadors meant that it took the Spanish some 170 years to finally conquer them.
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