6.0 Volcanoes and Human Settlement in the Northern Sierra of Ecuador

In Andean countries like Ecuador, the long sequence of human occupation has occurred concurrently with intermittent activity by the region's volcanoes. At least 17 volcanoes in Ecuador and southern Colombia have erupted in the course of the Holocene period (Hall and Mothes 1994; Mothes and Hall 1998b).

6.1 The eruption of Quilotoa

One such volcano, Quilotoa, some distance away in the Western Cordillera to the south of Quito, suffered a violent and explosive eruption in c. 800 BP. Its own distinctive ash 'signature' has been traced by researchers as far away as the northern sierra, where a layer of very fine ash covers extensive tracts of land and buried large areas of indigenous agricultural systems, including camellones, beneath them. Quilotoa ash has been found in a number of locations, mainly associated with infilled camellón and agricultural ditches at archaeological sites in and around the Cayambe region (see for example Athens 1998, 170-79). Further to the south of Cayambe, for example at Quito, it is believed that massive land-abandonment followed this eruption as dense accumulations of coarser ash and volcanic debris covered the settlements and their land rendering them useless (Villalba and Alvarado 1998, 73-110). Even now in present-day Quito it is possible to see the effects of this catastrophe preserved in the profiles of deep excavations made during the construction of modern tower blocks. The characteristic mounded ridges and 'u'-shaped ditches of the camellones appear as dark silhouettes covered by the whiteish ash.

Given that this event is now linked to the start of the Late Period it is appropriate to consider the evidence available for its date, summarised in the table below. Mothes and Hall usually refer to the date in their literature as 800 BP uncalibrated (1998b, 117). This 'ball-park' figure derives from uncalibrated radiocarbon dates from carbonised wood taken from the volcano's pyroclastic flow deposits, which vary from from 840 ±50 and 900 ±150 BP. However, a later AMS date of 785 ±50 BP is actually considered to be the more reliable (Mothes and Hall 1998b, 117). When calibrated to within a one sigma range the dates are 735-666 cal. BP and 790-688 cal. BP (cal. AD 1215-1284 and cal. AD 1160-1262 - Hall and Mothes 1994, 59-60). The three relevant 14C determinations from Hacienda Zuleta are 780 ±40 BP (cal. AD 1205-1290 at two sigma, intercept at cal. AD 1265) from charcoal immediately underlying the ash in an agricultural ditch and 770 ±40 BP (cal. AD 1185-1285 at two sigma, intercept at cal. AD 1255/BP 695) from charcoal present in the 'recovery' cultivation phase succeeding the eruptive event. Charcoal from within the pre-mound paleosol of a mound constructed with materials incorporating Quilotoa ash was dated to 883 ±80 BP (calibrated at two sigma to BP 950-680 intercept at BP 785; cal. AD 1000-1270 intercept at cal. AD 1165). It would seem, therefore, that the event itself has a terminus post quem of c. AD 1280-1290 and that Hall and Mothes 'ball-park' of 800 BP is, therefore, not unreasonable.

Provenance Conventional Age BP Calibrated Age x1 sigma Years BP Calibrated Age x1 sigma Years AD
Carbonised wood - Quilotoa pyroclastic flow deposits 840 ±50
Beta Analytic
735-666 1215-1284
Carbonised wood - Quilotoa pyroclastic flow deposits 900 ±150
790-688 1160-1262
Carbonised wood - Quilotoa pyroclastic flow deposits 785 ±50 AMS
nd nd
Hcda Zuleta: carbon from agricultural ditch, beneath Quilotoa tephra 780 ±40 AMS
Beta Analytic
nd 1235-1280
Hcda Zuleta: carbon from 'recovery' phase overlying Quilotoa tephra 770 ±40 AMS
Beta Analytic
730-675 1220-1275
Hcda Zuleta: carbon from palaeosol underlying mound containing Quilotoa tephra 883 ±80
921-709 1029-1241


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Last updated: Thu Apr 5 2001