Volcanoes - Extreme Events: A Physical Reconstruction and Risk Assessment - page 213

Table 8.3 Comparison between the battle of Zeus and the Titans and the likely sequence
of events during the eruption at Thera (from Greene, 1992 )

Hesiod's description (Zeus vs Titans) Eruption of Thera

A long war Premonitory seismicity

Both sides gather strength Increasing activity

Terrible echoes over the sea First phase explosions

Ground rumbles loudly Tectonic earthquakes

Sky shakes and groans Air shock waves

Mt Olympus trembles Great earthquakes

Steady vibrations of the ground Earthquakes

Weapons whistle through air Pyroclastic ejecta

Loud battle cries Explosive reports

Zeus arrives: lightning, thunder, fields, forests burn Volcanic lightning, heat of ignimbrites

Earth and sea boil Magma chamber breach

Immense flame and heat Phreatomagmatic explosion

Sound of earth/sky collapse Sound of above

Dust, lightning, thunder, wind Final ash eruptions

Titans buried under missiles Collapsed debris

Stratigraphy and tephrochronology

Stratigraphic methods are commonly used to identify, analyse and date
episodes of volcanic activity. Stratigraphic units can include lavas, pyroclastic
deposits, tuffs (sedimentary deposits eroded from volcanic rocks), and pumice
and ash fall deposits. The stratigraphy can be analysed where streams have cut
into the sequence and also from cores. Grain-size, lithological and geochemical
analyses of individual units help to determine the origin and age of eruption
events. The stratigraphy of ice cores in the Arctic region and Antarctica can
even reveal the age and sometimes the location of large distant eruptions when
ash has entered the upper atmosphere. Stratigraphic analysis is probably the
most reliable of all methods in accurately reconstructing the long-term history
of volcanic activity of an area. A variety of dating techniques can be used includ-
ing radiocarbon, isotopes and luminescence depending upon the quality of the
preserved materials (Lecointre et al ., 2002).
Tephrochronology is the study of tephra layers in stratigraphic sequences.
Comparison of the tephra's chemical components with modern analogues helps
to identify the specific volcano or the volcanic field from which the layer orig-
inated. Dating of the layer, or those immediately above and below, depending
upon the nature of materials in the stratigraphic sequence, can determine the
age of the eruption. Tephra layers can mark both local and distant volcanic