Walking through volcanic mud: the 2,100 year-old Acahualinca footprints (Nicaragua) II: the Acahualinca people, environmental conditions and motivation

Abstract

We analyzed bare human footprints in Holocene tuff preserved in two pits in the Acahualinca barrio in the northern outskirts of Managua (Nicaragua). Lithology, volcanology, and age of the deposits are discussed in a companion paper (Schmincke et al. Bull Volcanol doi: 10.1007/s00445-008-0235-9, 2008. The footprint layer occurs within a series of rapidly accumulated basalticandesitic tephra that is regionally correlated to the Masaya Triple Layer Tephra. The people were probably trying to escape from a powerful volcanic eruption at Masaya Caldera 20 km farther south that occurred at 2.1 ka BP. We subdivided the swath of footprints, up to 5.6 m wide, in the northern pit (Pit I) into (1) a central group of footprints made by about six individuals, the total number being difficult to determine because people walked in each other's footsteps one behind the other and (2) two marginal groups on either side of the central group with more widely spaced tracks. The western band comprises tracks of three adjacent individuals and an isolated single footprint farther out. The eastern marginal area comprises an inner band of deep footprints made by three individuals and, farther out, three clearly separated individuals. We estimate the total number of people as 15-16. In the southern narrow and smaller pit (Pit II), we recognize tracks of ca. 12 individuals, no doubt made by the same group. The group represented in both pits probably comprised male and female adults, teenagers and children based on differences in length of footprints and of strides and depth of footprints made in the soft wet ash. The smallest footprints (probably made by children) occur in the central group, where protection was most effective. The footprint layer is composed of a lower 5-15-cm thick, coarse-grained vesicle tuff capped by a medium to fine-grained tuff up to 3 cm thick. The surface on which the people walked was muddy, and the soft ash was squeezed up on the sides of the foot imprints and between toes. Especially, deep footprints are mainly due to local thickening of the water-rich ash, multiple track use, and differences in weight of individuals. The excellent preservation of the footprints, ubiquitous mudcracks, sharp and well-preserved squeeze-ups along the margins of the tracks and toe imprints, and the absence of raindrop impressions all suggest that the eruption occurred during the dry season. The people walked at a brisk pace, as judged from the tight orientation of the swath and the length of the strides. The directions of a major erosional channel in the overlying deposits that probably debouched into Lake Managua and the band of footprints are strictly parallel, indicating that people walked together in stride along the eastern margin of a channel straight toward the lake shore, possibly a site with huts and/or boats for protection and/or escape.

The Malpaisillo Formation: A sequence of explosive eruptions in the mid to late Pleistocene (Nicaragua, Central America)

“…It was revisited and complemented by Kutterolf et al (2007 and references therein) comprising now 15 tephra layers, which were ordered into two stratigraphic groups according to their volcanic sources. To the south, the Managua-Masaya Group includes the younger, Upper Pleistocene Managua, and the older Las Sierras Formations (Apoyo and Masaya Calderas; Freundt et al, 2006aFreundt et al, , 2006bFreundt et al, , 2010Kutterolf et al, 2007;Peréz et al, 2009;Schmincke et al, 2010Schmincke et al, , 2009Wehrmann et al, 2006Wehrmann et al, , 2016. The latter has been estimated to be older than~30 ka (Kutterolf et al, 2007(Kutterolf et al, , 2008aSchindlbeck et al, 2016aSchindlbeck et al, , 2016b.…”

Footprints and human evolution: Homeostasis in foot function?

“…Within the geological record, human footprints (tracks) occur infrequently as result of rare occurrences of sedimentary preservation (Aldhouse-Green et al, 1993;Roberts et al, 1996;Allen, 1997;Avanzini et al, 2008;Lockley et al, 2008;Kim et al, 2009;Schmincke et al, 2009Schmincke et al, 2010. Each set of tracks holds a potential glimpse into the locomotive behaviour of the track-maker.…”

The composition of a Neandertal social group revealed by the hominin footprints at Le Rozel (Normandy, France)

“…Fossil footprints are preserved when rapidly buried and thus represent a snapshot of life (e.g., refs. [14][15][16]. As such, ichnological assemblages give the opportunity to directly investigate hominin group size and composition, based on trackways (e.g., refs.…”