 |
| Titel |
Syn-eruptive, soft-sediment deformation of deposits from dilute pyroclastic density current: triggers from granular shear, dynamic pore pressure, ballistic impacts and shock waves |
| VerfasserIn |
G. A. Douillet, B. Taisne, È. Tsang-Hin-Sun, S. K. Müller, U. Kueppers, D. B. Dingwell |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1869-9510
|
| Digitales Dokument |
URL |
| Erschienen |
In: Solid Earth ; 6, no. 2 ; Nr. 6, no. 2 (2015-05-21), S.553-572 |
| Datensatznummer |
250115450
|
| Publikation (Nr.) |
 copernicus.org/se-6-553-2015.pdf |
|
|
|
|
|
| Zusammenfassung |
Soft-sediment deformation structures can provide valuable information about
the conditions of parent flows, the sediment state and the surrounding
environment. Here, examples of soft-sediment deformation in deposits of
dilute pyroclastic density currents are documented and possible syn-eruptive
triggers suggested. Outcrops from six different volcanoes have been compiled in
order to provide a broad perspective on the variety of structures:
Soufrière Hills (Montserrat), Tungurahua (Ecuador), Ubehebe craters (USA),
Laacher See (Germany), and Tower Hill and Purrumbete lakes (both Australia).
The variety of features can be classified in four groups: (1) tubular features
such as pipes; (2) isolated, laterally oriented deformation such as overturned
or oversteepened laminations and vortex-shaped laminae; (3) folds-and-faults
structures involving thick (>30 cm) units; (4) dominantly vertical
inter-penetration of two layers such as potatoids, dishes, or diapiric
flame-like structures.
The occurrence of degassing pipes together with basal intrusions suggest
fluidization during flow stages, and can facilitate the development of other
soft-sediment deformation structures. Variations from injection dikes to
suction-driven, local uplifts at the base of outcrops indicate the role of
dynamic pore pressure. Isolated, centimeter-scale, overturned beds with vortex forms
have been interpreted to be the signature of shear instabilities occurring at
the boundary of two granular media. They may represent the frozen record of
granular, pseudo Kelvin–Helmholtz instabilities. Their recognition can be a
diagnostic for flows with a granular basal boundary layer. Vertical
inter-penetration and those folds-and-faults features related to slumps are
driven by their excess weight and occur after deposition but
penecontemporaneous to the eruption. The passage of shock waves emanating
from the vent may also produce trains of isolated, fine-grained overturned
beds that disturb the surface bedding without occurrence of a sedimentation
phase in the vicinity of explosion centers. Finally, ballistic impacts can
trigger unconventional sags producing local displacement or liquefaction.
Based on the deformation depth, these can yield precise insights into
depositional unit boundaries. Such impact structures may also be at the
origin of some of the steep truncation planes visible at the base of the
so-called "chute and pool" structures.
Dilute pyroclastic density currents occur contemporaneously with seismogenic
volcanic explosions. They can experience extremely high sedimentation rates
and may flow at the border between traction, granular and fluid-escape
boundary zones. They are often deposited on steep slopes and can incorporate
large amounts of water and gas in the sediment. These are just some of the
many possible triggers acting in a single environment, and they reveal the
potential for insights into the eruptive and flow mechanisms of dilute
pyroclastic density currents. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|