free download - University Press of Colorado

Chapter 3
Black Sun, High Flame, and Flood:
Volcanic Hazards in Iceland
Andrew Dugmore and Orri Vésteinsson
University of Edinburgh and University of Iceland
Chapter Abstracts
People in Iceland have lived (and died) with volcanic hazards for over 1,150
years. These hazards can be broadly grouped into fout types: those from volcanic
fallout (ash fall and pyroclastic flows), floods (of water melted from glaciers
or dammed in rivers and lahars), lava, and pollution (poisoning from carbon
mo noxide and fluorine). They occur at irregular intervals and often widely separated
times—maybe once or twice a generation, maybe once a millennium.
When volcanic hazards do occur, their scale may be comparatively limited—
affecting a small region for a short time—or their effects may be persistent and
felt both across the entire island and much farther afield. Long recurrence times
have meant there may be little specific planning to cope with volcanic impact.
The potential human impacts of volcanic eruptions do not depend on the
size and type of eruption alone; the environmental and social context is vital.
Few volcanic eruptions have directly or indirectly killed people, but when bad
synergies occur, death tolls can be great.
Historically, communal resilience in Iceland that developed to face other
environmental challenges, such as extreme weather, has been the basis of effective
response to volcanic hazards and the mitigation of their impacts. Today,
volcanic emergency planning in Iceland has specific provisions based on
detailed geological assessments. The modern science of volcanic hazard assessment
faces a number of specific challenges over establishing the nature of possible
events and their potential impacts. Some past volcanic events have left clear
traces behind, such as a layer of volcanic ash or a characteristic flood deposit.
Other hazards, such as fluorine poisoning of livestock, leave no direct evidence,
and their occurrence has to be inferred indirectly through, for example, studies
of magma composition (to infer the presence of a volatile element) or written
records of deaths of livestock or people. Even when there is direct physical
evidence, such as the landscape record of a flood, it may be ambiguous. Was it
from a volcanic event How big was the event
Serendipitously, the volcanic events that create hazards in Iceland have
also created a very effective means of assessing those hazards. Volcanic eruptions
frequently create extensive layers of volcanic ash (tephra) that are rapidly
spread across the landscape. These deposits form marker horizons that are
incorporated into the rapidly aggrading aeolian soils. We can identify, correlate,
and date these tephra deposits; reconstruct extensive synchronous horizons;
and use them to gain precise knowledge of past hazards: their magnitude,
extent, and impact. The tephras themselves may be the hazard; we can tell if
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