Tephrochronology, landscape and population: impacts of plague on medieval Iceland
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Date
25/06/2012Author
Streeter, Richard Thomas
Metadata
Abstract
This thesis examines the extent to which geomorphological change in sub-arctic
landscapes may be driven by rapid declines in population over timescales of
decades to centuries. Demographic decline driven by disease in pastoral agricultural
systems is expected to alter patterns of land use. Using a chronology
with 20 visible dated tephra layers from AD 870 to present, 2625 tephra layers
were identified in 200 sediment profiles. Rates of sediment accumulation
dated by tephra provide a record of erosion in Skaftártunga, South Iceland. The
scale of enquiry is that of individual landholdings (5–10 km2) over decades to
centuries; in order to tackle questions of resilience and change within coupled
socio-ecological systems larger and smaller spatial scales (regions of 400 km2 and
individual sediment profiles) and longer and shorter temporal scales (2.6 ka and
years to decades) are also considered. The novel application of photogrammetric
techniques to recording stratigraphic sections increases the frequency of measurement
from tens to hundreds per stratigraphic unit and the resolution from ±2.5
mm to ±1 mm. This technique improves the accuracy of representative measures
of sediment accumulation and their use in measuring landscape change. Two
little known 15th century AD Grímsvötn tephras are mapped and dated to AD
1432±5 and AD 1457± 5 using sediment accumulation rates. A period of landscape
stability from AD 1389–1597 is consistent with reduced grazing pressure
due to population declines of more than 30% after plague in AD 1402–1404 and
AD 1494. Climatic deterioration from AD 1450-1500 does not increase erosion
as much as expected; this may be due to decreased grazing pressure after population
decline in the 15th century. Increased erosion from AD 935–1262 is related
to woodland clearance and increases in sediment accumulation post AD 1625 are
related to climatic cooling during the Little Ice age and the migration of erosion
fronts into deep lowland sediments.