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Lidar technology reveals the magnitude of Palau's ancient terraces


Drone lidar image of a massive terrace complex in Aimeliik. Largely covered in dense forest, laser pulses were able to penetrate the vegetation to reveal the ancient earthwork underneath. This type of structure may have supported a hamlet or village with integrated residential, agricultural, ceremonial, and activity areas.

By Jolie Liston

 

Koror-- The thick tropical vegetation covering Babeldaob has long hidden the true extent of Palau’s ancient cultural landscape.


Recently, laser technology called lidar has been used to visually remove the dense tree canopy and reveal the vast extent, massive size and diverse shapes of the island’s earth architecture.


The magnitude of terraces (oblallang) revealed is remarkable, with at least 21 square miles (17.4 percent) of Babeldaob presently known to be covered by these ancient Palauan-built earthworks.


This number is sure to rise dramatically as surveys with higher-resolution lidar that can better penetrate the dense forests covering the island’s rugged interior are completed.

 

  Airplane lidar image of Ngerchelong showing the huge area covered in terraces. Some of Babeldaob’s almost 300 known crowns (steep-sided, flat-topped high points) are visible in the picture. Image courtesy of Palaris

Lidar (light detection and ranging) technology creates detailed, three-dimensional maps of the ground surface using pulses of laser light released from a sensor carried on an airplane or a drone.


The measurements are taken using the time the laser takes to hit a solid surface and bounce back to the sensor. While most of the millions of laser pulses emitted per second hit vegetation, enough reach the ground to map Babeldaob’s surface.


 With the support of the U.S. Ambassadors Fund for Cultural Preservation, Guam-based Pacific UAV Corp. (2cofly) in partnership with Bella Wings Aviation recently carried out a drone-based lidar survey of 2,400 acres in Aimeliik to map the terraced landscape.


Their work improves on Palau’s previous plane-based lidar surveys. As a drone flies much slower and lower than a plane, considerably more laser points hit the ground to reveal terracing in areas that are blurred in the previous data sets.

 

Although modifications to the landscape likely began soon after Palau’s colonization about 3,500 years ago, archaeological evidence indicates that by at least 2,400 years ago elaborate terrace construction was underway.


Using only simple tools such as digging sticks and baskets, hills and slopes were sculpted into the huge earth structures we still see today.


This amazing human effort would continue for over 1300 years to create a remarkable cultural landscape unequaled anywhere else in the Pacific.


During this time, the terraces supported the majority of community activities, being used for habitation, infrastructure, agriculture, defense, and ceremonies and rituals.

 

The full scope of the engineered landscape shows Palau’s cultural significance in ancient Oceania and ranks among the world’s most impressive monumental architecture.


Melanesia and Polynesia also have earthworks, but the Palauan accomplishments are far beyond anything else done in the entire Pacific region.


Only in Palau does the terracing connect to form up to 8 square mile clusters of earthworks.


Researchers interpret these groupings as sociopolitical districts whose power was symbolized by the immense size of their earth architecture.


Step-terraces and ditches descend up to 20 feet and the steep-sided, flat-topped high points (“crowns”) rise as much as 40 feet above the surrounding slopes.

 

Demonstrating the ability to organize, finance, and manage the large labor force needed, monumental architecture is associated with increasing sociopolitical complexity.


Palau’s earthworks were enormous in size and extent some 2000 years ago, perhaps 800 years before any other Pacific society began to produce such large structures.

 

Palau’s earthwork landscape is an architectural marvel, built with sophisticated cut-and-fill techniques and still standing a thousand years after its construction. This demonstrates the expertise of early Palauans in soil mechanics, hydrogeological conditions, and engineering principles.


Sustaining the inland cultivation system for over a thousand years, while managing the erosion and sedimentation during deforestation and terrace construction and use, is a testament to ancient Palauan effective and intensive land management strategies.

 

Dr. Jolie Liston is an archeologist. Along with the Coral Reef Research Foundation, Liston has received a grant from the U.S. Ambassadors Fund for Cultural Preservation for Preserving the Legacy of a Monumental Earthwork Landscape Project in Palau."




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