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Groundwater environments
Published in Ian Acworth, Investigating Groundwater, 2019
The most well-established hot spot volcano is considered to be Hawaii. There has been a lot published about this system and the trail (Figure 1.33) it has left. The volcano must make use of a pre-existing weakness to establish a conduit to the surface through the plate. This conduit must be a little elastic, as it remains active for a few million years before finally being snapped and volcanic activity begins again at another location. The initial volcanic activity is in the form of an underwater vent on the sea bed with basalts that form what are known as pillow lava. These build up as an underwater cone until finally the vent breaks the surface and the volcano continues to build above sea level. Pyroclastic material is not washed away and the volcano grows more rapidly. A full shield-type volcano can result with the final vent more than 3000 m above sea level.
Plutonic Rocks
Published in Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough, Earth Materials, 2019
Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough
A “complete” ophiolite, something that is uncommon, includes all the layers of rock shown in Figure 6.30. These layers correspond to the sediments and rocks being created by seafloor spreading at mid-oceanic ridges and make up a cross section of the oceanic lithosphere. At its top, the lithosphere is overlain by muds and other sediments that may lithify to form shale or chert. These sediments increase in thickness from mid-ocean ridges to ocean margins. Beneath the sedimentary layers, the rocks are all igneous rocks. A layer of basalt, often containing pillow lavas that form tube-like bodies when lavas erupt on the ocean floor, underlies the sediments. These basalts, like many ocean floor basalts, are highly altered by interaction with seawater.
Magmatism and Magmatic Rocks
Published in Aurèle Parriaux, Geology, 2018
At depth, magmas form mafic and ultramafic plutonic rocks at the base of the plate. Submarine volcanic flows form the ocean floor, creating pillow lava at the surface (Fig. 6.32) and columnar basalts below (Fig. 6.20).
Pre-1.94 to post-1.88 Ga sediment depositional environment and c. 1.94 Ga felsic magmatism in the Knaften area, northern Sweden
Published in GFF, 2019
Annika Wasström, Hannu Huhma, Raimo Lahtinen, Jenny Andersson, Fredrik Hellström
Approximately 600 m north and east and 1 km south (Fig. 4) of the site of the sandstone sample (A2334), mafic to intermediate resedimented volcaniclastic rocks intercalated with turbiditic sedimentary rocks occur. About 1 km north-northeast of the same site there are well-preserved isolated broken pillow lava fragments (Fig. 5B) among volcanic breccias and volcaniclastic rocks intercalated with sedimentary rocks. Discordant bedding, filled channels and imbrication of clasts upstream the debris flow (Fig. 5E) can also be seen in these deposits.
Contemporaneously emplaced submarine volcaniclastic deposits and pillow lavas from multiple sources in the island arc Brook Street Terrane, Southland, New Zealand
Published in New Zealand Journal of Geology and Geophysics, 2020
Jasmine F. Mawson, James White, James Michael Palin
Pillow lava displays the prominent pillow lava morphology of sack-like forms filling into depressions between underlying pillows (Table 1); in a few localities the outcrop is sufficiently three-dimensional to reveal the elongate lateral sides of the pillows. Glassy pillow rinds are commonly absent, but in a few places they are represented by a 1–2 cm band of darker coloured, sometimes reddish, rock with cracks between it and the body of the pillow.