Thread by @philriris

So I've broken the 1k follower mark (h/t @JacquelynGill), and I've recently wrapped up fieldwork surveying #rockart in the Colombian Amazon. What better way to celebrate both than a thread of my favourite fieldwork snaps from the Guaviare River? (1/20

The Guaviare is a mighty river that rises in the Andes and flows west-to-east into the Orinoco, eventually emptying into the Atlantic. I was working (along with Colombian colleagues not on Twitter) near the Guayabero confluence, an unusual hilly area of narrows and rapids (2/

Brief background: we aimed to create an in situ record of known rock art sites in the region. To do this, we used structure-from-motion photogrammetry to make to-scale 3D reconstructions of panels from sets of 2D photographs. The Guaviare is extremely dense in sites... (3/

...including the nearby UNESCO World Heritage Site of Chiribiquete, which sadly was off limits to us due to local FARC dissident unrest and general inaccessibility. We did take 2200+ photos (~26 GBs) from 17 discrete painted #rockart panels, so still plenty to work with! (4/

First, one of the better-known sites: the main panel at Cerro Azul, which I have tweeted previously. Despite its obvious grandeur, the motifs tend to respect each other (no overlap), making it challenging to interpret in even relative chronological terms (5/

Next, also on Cerro Azul, my personal favourite: the panel of the tapirs, named so for the two giant tapirs facing each other! (6/

This panel is especially interesting because more than any other, it seems to tell little stories or vignettes - possible scenes of hunting (including extinct megafauna), sex, and processions all figure... it feels very human. (7/

Geometric motifs - shapes whose precise meaning(s) have been lost to time - predominate in general, but the panel of the tapirs is also notable for its naturalistic aspect. Here, couples and families (8/

Another cool thing about Cerro Azul (yes yes we'll move on in a sec) is the half-lifesize motif of a human figure, located above a burial which dates to the pre-Conquest ceramic period. Much older dates are also known - these sites may have been used for a very long time! (9/

SIDE NOTE: you may see little black-and-white labels in some photos. These are photogrammetric targets we attached to blank areas of the panels, with gentle, non-damaging, biodegradable tack. They allow us to accurately reconstruct the real size of the art. (10/

Next, I must emphasise that these are BIG sites - and believe me, I am no stranger to very large rock art! A paper published in @AntiquityJ a couple of years ago (open access) had HUGE individual motifs, but here it's the sites that impress doi.org/10.15184/aqy.2… (11/

How big? Hard to say, as many motifs have been lost to lichen growth and exposure. However, scraps of paint between preserved groups of motifs all along Panel 5 at the Don Barbas (pictured) site, suggests that it may once have been almost 100m long. (12/

The sizes of sites can make them visible from far away, as here in Nuevo Tolima. I say *can* because in all likelihood the pre-Columbian vegetation pattern was closed-canopy rainforest that hid panels from direct view (and exposure).... (13/

...but this does not necessarily mean that sites couldn't have spectacular views themselves under the right conditions. Vegetation cover, however, may be integral to their preservation AND creation! (14/

What do I mean by this? Loads of motifs are well above head height - how were they made? A possible answer: using the extant vegetation to climb, just as we did to access some sites! These aren't trunks, but the aerial roots of plants embedded in niches above rockshelters! (15/

Inaccessibility is a common theme among sites - they are found on steep, high ground, at the bases of the summits of tepuies (table mountains), in very dense forest. But their creators must have been familiar with the terrain - motif superimposition implies repeat visits! (16/

This is no longer always the case. Many (here, Puerto Lucas) are now touristic sites, which opens them up to a number of risks to their integrity and conservation. I myself have noticed differences between mine and my colleagues' recent photos. The #rockart is in danger. (17/

This is a major reason why it's critical to have accurate records of site condition, and it's a big driver of why I do what I do. Clearing of vegetation to enable access also causes exposure to sun and rain, further damaging these incredible, unique sites. (18/

This has become very long so I'll end it there. None of what I've shown has been a solo effort. Thanks to generous @BritishAcademy_ funding, and support from my colleagues Natalia Lozada (U Los Andes, pictured) and Gaspar Morcote (U Nacional), this research was possible. (19/

Furthermore, the hospitality, generosity, and warmest imaginable welcome from Don Nelson Castro and his family in Raudal Guaybero is what really made this fieldwork tick. My deepest thanks to them, and all of our guides! End. (20/20)