Surface Erosion and Mass Movement Constrains in the Conservation of Akapana Pyramid Mound (Tiwanaku, Bolivia)

Abstract

Tiwanaku is an Archaeological World Heritage Site, located at an elevation of 3,885m.a.s.l., south of Lake Titicaca, in the altiplano or high plateau region of the Republic of Bolivia. It is in the province of Ingavi, department of La Paz, 60km from the city of La Paz. Major highlight of the site is the Akapana pyramid, an extensive earth mound hill, with only few remaining of the original coverage of stone and coloumns.

The pyramid is suffering for extensive erosional phenomena such as: rill erosion, mass movement and creeping;

The majority of the phenomena mentioned above are caused by the uncontrolled flow of the rainwater, which flows freely through the depressions (natural or cultural) but which, also, infiltrates and deforms the materials of the deposits and appears to be affecting the stability of the internal structures. From site inspeciton it is possible to note the large toe deposit originated by the erosion/dismantling of the earth mound, some potential surficial mass movement and creeping and the evidence of deformed walls, suggesting internal deformation to the mound. Also, in grey is the large rubble left from the excavation of the Colonia Period.

With reference to the erosion of the mound, there is a clear evidence (rill erosion and small valleys on the mound) that a large part of the original structure has been affected by erosion and deposited at the base or foot of the pyramid; moreover, it is not possible to exclude that the stepped design in the shape of the “chacana” or Andean cross could have played some roles in such erosion.

The present paper is showing major erosional problems and suggesting mitigation measurements, possibly based on local traditional techniques.