Siegfried Siegesmund - Monument Future

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Christopher Pötzl 1 , Ali D. Öcal 2 , Thomas Cramer 3 , Siegfried Siegesmund 1

IN: SIEGESMUND, S. & MIDDENDORF, B. (EDS.): MONUMENT FUTURE: DECAY AND CONSERVATION OF STONE.

– PROCEEDINGS OF THE 14TH INTERNATIONAL CONGRESS ON THE DETERIORATION AND CONSERVATION OF STONE –

VOLUME I AND VOLUME II. MITTELDEUTSCHER VERLAG 2020.

1Geoscience Centre of the Georg August University Göttingen, Germany

2Department of Anthropology of the National University of Colombia, Bogota, Colombia

3Department of Geosciences of the National University of Colombia, Bogota, Colombia

The pre-Columbian astronomical and meteorological observatory of El Infiernito or ‘Little Hell’ is situated within the Monquirá Archaeological Park, near the colonial town of Villa de Leyva in the Colombian Boyacá-Department. Several burial mounds and a variety of phallic-shaped monoliths, made of local sandstone, bear witness to the culture and unique masonry of the ancient Muisca culture. The El Infiernito ranks among the most important historical and cultural monuments in Colombia. The monoliths were erected nearly two millennia ago and show severe damages today that developed over the time since its construction. Depending on their exposition, various weathering phenomena like differential back-weathering, scaling, cracking and discoloration can be observed. In order to identify the main damage causes and understand their relation with the stone properties, in-situ investigations, in the form of lithology and damage mapping, as well as laboratory work regarding petrography, petrophysical properties and weathering behavior of four sandstones were done. The research demonstrates the differential weathering behavior of the analyzed sandstones and identifies thermal and thermohygric expansion as the main weathering agents.

Keywords: Colombia, El Infiernito, monoliths, sandstone decay, damage assessment, weathering processes

The stone monoliths at El Infiernito (Fig. 1) have been the subject of much attention ever since the earliest Spanish missionaries, because of their claimed associations with controversial Muisca rituals and alleged riotous ceremonies (Simon 1981). The arrangement of 26 finely carved and equidistant cylindrical pillars in two parallel rows led Silva Celis (1981) to the conclusion that the archaeological 210site had been a sacred field of astronomical and meteorological observation. The natives had measured the movements of the sun, and thus, solstices and equinoxes were calculated and periods of rain and drought were established, which regulated the production activities of the natives (Silva Celis 1981). A dolmen tomb found in 2006 together with 54 phallic-formed sandstone monoliths and indications of feasting events, suggest that El Infiernito was a central place where inter-community activities were carried out.

Figure 1: General view of the archaeological park.

In this study, preliminary results of an investigation on the main characteristics of the deterioration processes that affect the monoliths of the Monquirá archaeological park El Infiernito are presented. This work will serve as a base for later conservation and restoration activities.

The exposed monoliths present significant problems due to the environmental conditions (Öcal et al. 2009) and show diverse, partly exposure-specific forms of weathering (Fig. 2). Approximately 200 monoliths and stone columns were used to visually assess and characterize the weathering behavior.

Figure 2: Decay phenomena on the monoliths. a) biological colonization and sanding, b) crust formation and salt efflorescence, c) alveolization, d) scaling.

The tropical climate at the ~2000 m a. s. l. El Infiernito area is characterized by two rainy and two dry seasons. The rainiest months are May and October with up to 200 mm, whereas January is the driest month with 40 mm followed by July with 90 mm. In addition to the rain, in the mostly semiarid microclimate, air humidity plays an important role as a water supplier. The relative air humidity fluctuates between 70–85 % depending on the season. Direct water absorption during rain events or capillary suction of surface and soil water, control the humidity regime. The monthly average temperatures are above 20 °C throughout the year, with lowest mean temperatures of 10 °C and highest mean temperatures of 22 °C and can rise to over 30 °C. Especially during the long dry and cloudless seasons, the temperatures on the monoliths’ surface can reach high values.

The monoliths show a large variety of different damage types, such as relief, back-weathering, bursting, rounding, covings and alveolization, which predominantly occurs. Neighboring areas of the stone surface weather back to different degrees, and create a moving relief, e. g. by weathering parallel to the layer or by the loss of components. Often honeycomb-like structures are formed, which are typical for alveolar weathering (Fig. 2c). The causes can be of a very different nature. These can include salt weathering and wind erosion, as well as structural and lithological peculiarities.

The deposition of dirt and dust particles in the pore space leads to a gradual compaction of the rock surface, and may favor biological growth on some monolith surfaces. Gray to brownish crusts (Fig. 2b) can be found on the stone surface as coherent layers, millimeter to centimeters thick. Visually, the limit between the natural patina and the damage pattern crust cannot always be clearly determined. Biological colonization by green algae, lichens and higher plants was observed on all monoliths (Fig. 2a). Loosely adhering whitish salt efflorescence is an indication of the build-up of harmful salts enriched in the stone (Fig. 2b).