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Widespread inflation and drainage of a p?hoehoe flow field: the Nesjahraun, Þingvellir, Iceland

Widespread inflation and drainage of a p?hoehoe flow field: the Nesjahraun, Þingvellir, Iceland
Widespread inflation and drainage of a p?hoehoe flow field: the Nesjahraun, Þingvellir, Iceland
This study describes the emplacement of the Nesjahraun, a basaltic lava flow that entered the lake Þingvallavatn, SW Iceland. High-resolution remotely sensed data were combined with fieldwork to map the flow field. Onshore, the Nesjahraun exhibits a variety of textures related to the widespread inflation and collapse of a p?hoehoe flow field. Its emplacement is interpreted as follows: Initially, the eruption produced sheet p?hoehoe. In the central part of the flow field, the lava has a platy-ridged surface, which is similar to some other lava flows in Iceland and on Mars. Here, the texture is interpreted to have formed by unsteady inflation of the brittle crust of stationary sheet p?hoehoe, causing it to break into separate plates. The ridges of broken p?hoehoe slabs formed as the plates of crust moved vertically past each other in a process similar to the formation of shatter rings. Upstream, fresh lava overflowed repeatedly from channels and tubes, covering the surface with shelly p?hoehoe. Formation of a 250-m-wide open channel through the flow field allowed the inflated central part of the flow to drain rapidly. This phase produced ‘a‘? lava, which eroded the channel walls, carrying broken p?hoehoe slabs, lava balls and detaching large (>200 m long) rafts of compound shelly p?hoehoe lava. Much of this channelized lava flowed into the lake, leaving a network of drained channels and tubes in the upstream part of the flow. As in other locations, the platy-ridged texture is associated with a low underlying slope and high eruption rate. Here, its formation was possibly enhanced by lateral confinement, hindered entry into the lake and an elevated vent location. We suggest that formation of this type of platy-ridged lava, where the plates are smooth and the ridges are slabs of broken p?hoehoe, can occur without significant horizontal transport, as the surface crust is broken into plates in situ. This reconstruction of the emplacement of the Nesjahraun also demonstrates that high-resolution aerial survey data are extremely useful in the mapping and measurement of lithofacies distributions in large flow fields, but that fieldwork is still necessary to obtain the detailed textural information necessary to interpret them.
LiDAR, Lava, Iceland, Platy-ridged lava, Inflation, Shelly p?hoehoe
0258-8900
15-31
Stevenson, John Alexander
e8103350-06b5-435a-a3fa-d3e8d9fab61c
Mitchell, Neil Charles
ebead8cf-46d8-401a-a7cf-9ef3c04a6b58
Cassidy, Michael
fc0e9729-9c71-477d-a4e3-39698155e6fc
Pinkerton, Harry
e11f5f9f-bb6d-4faa-bb4f-b33607fcc58a
Stevenson, John Alexander
e8103350-06b5-435a-a3fa-d3e8d9fab61c
Mitchell, Neil Charles
ebead8cf-46d8-401a-a7cf-9ef3c04a6b58
Cassidy, Michael
fc0e9729-9c71-477d-a4e3-39698155e6fc
Pinkerton, Harry
e11f5f9f-bb6d-4faa-bb4f-b33607fcc58a

Stevenson, John Alexander, Mitchell, Neil Charles, Cassidy, Michael and Pinkerton, Harry (2012) Widespread inflation and drainage of a p?hoehoe flow field: the Nesjahraun, Þingvellir, Iceland. Bulletin of Volcanology, 74 (1), 15-31. (doi:10.1007/s00445-011-0482-z).

Record type: Article

Abstract

This study describes the emplacement of the Nesjahraun, a basaltic lava flow that entered the lake Þingvallavatn, SW Iceland. High-resolution remotely sensed data were combined with fieldwork to map the flow field. Onshore, the Nesjahraun exhibits a variety of textures related to the widespread inflation and collapse of a p?hoehoe flow field. Its emplacement is interpreted as follows: Initially, the eruption produced sheet p?hoehoe. In the central part of the flow field, the lava has a platy-ridged surface, which is similar to some other lava flows in Iceland and on Mars. Here, the texture is interpreted to have formed by unsteady inflation of the brittle crust of stationary sheet p?hoehoe, causing it to break into separate plates. The ridges of broken p?hoehoe slabs formed as the plates of crust moved vertically past each other in a process similar to the formation of shatter rings. Upstream, fresh lava overflowed repeatedly from channels and tubes, covering the surface with shelly p?hoehoe. Formation of a 250-m-wide open channel through the flow field allowed the inflated central part of the flow to drain rapidly. This phase produced ‘a‘? lava, which eroded the channel walls, carrying broken p?hoehoe slabs, lava balls and detaching large (>200 m long) rafts of compound shelly p?hoehoe lava. Much of this channelized lava flowed into the lake, leaving a network of drained channels and tubes in the upstream part of the flow. As in other locations, the platy-ridged texture is associated with a low underlying slope and high eruption rate. Here, its formation was possibly enhanced by lateral confinement, hindered entry into the lake and an elevated vent location. We suggest that formation of this type of platy-ridged lava, where the plates are smooth and the ridges are slabs of broken p?hoehoe, can occur without significant horizontal transport, as the surface crust is broken into plates in situ. This reconstruction of the emplacement of the Nesjahraun also demonstrates that high-resolution aerial survey data are extremely useful in the mapping and measurement of lithofacies distributions in large flow fields, but that fieldwork is still necessary to obtain the detailed textural information necessary to interpret them.

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More information

Published date: 2012
Keywords: LiDAR, Lava, Iceland, Platy-ridged lava, Inflation, Shelly p?hoehoe
Organisations: Geochemistry

Identifiers

Local EPrints ID: 338935
URI: http://eprints.soton.ac.uk/id/eprint/338935
ISSN: 0258-8900
PURE UUID: f8eba96c-6b85-467f-98a0-d86dbe2f9ce6

Catalogue record

Date deposited: 17 May 2012 14:38
Last modified: 16 Jul 2019 22:03

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