Year: 1995
Type: dissertation
Abstract: Methods and concepts that may be used to quantitatively assess the lava emplacement mechanics, magma degassing, and environmental impacts flood basalt volcanism are presented.The structural characteristics and emplacement mechanics of flood basalt lavas are evaluated by studies of -15.3 Ma Levering (Grande Ronde Formation) and the -14.5 Ma Roza (Wanapum Formation) pahoehoe lava fields in the Columbia River Basalt Group.This evaluation is augmented by similar studies on several large pahoehoe lava fields in Iceland.Vertical distribution of textural properties, vesiculation features, and joint patterns in pahoehoe sheet flows defines three main structural components: the basal zone, the lava core, and the lava crust.These structural components are identified in pahoehoe sheet flows of all dimensions, suggesting that the same basic fluid dynamic processes govern their formation and are independent of lava flow size and volume.Structures of flood basalt lavas comply with dominance of endogenous processes during lava emplacement, such as internal lava injection and inflation.Consequently, a sustained input of liquid lava during a long-lived eruption resulted in sequential emplacement of lava lobes and flow units that progressively contributed to the enlargement of the lava flow field.The lava crust on an active pahoehoe flow unit thickens steadily during formation and laws of conduction predict that the final thickness of the lava crust is a function the total time that elapsed from the onset of flow unit emplacement until flowage of liquid lava through the core stops.Hence, the cumulative thickness of lava crusts in a particular lava flow, field measure the total duration of lava emplacement.Application of this concept indicates the Roza lava flow field formed over a period of 5-15 years.The duration of the Roza eruption suggests that anyone lava flow field within the CRBG may have been formed over periods of months to years,Table of
Author: T. Thórdarson
Language: English
Subfield: Geochemistry and Petrology
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W154017578