Volcanic ejecta

The materials that accumulate to form sedimentary rocks are (i) products of disintegration (weathering) of rocks, (ii) volcanic ejecta, (iii) insoluble decomposition products, (iv) precipitated substances from aqueous solutions, and (iv) bio-organically derived substances. 

Evidence also exists for a terrestrial source of the iridium enrichment as volcanic ejecta is enriched in this rare element. Thus, the enriched sediment layer could also have been caused by an abrupt and large increase in volcanic activity. Evidence for this is suggested by high levels of volcanic ash, soot, and shocked minerals in the iridium-enriched layer. Other geochemical characteristics of this sediment layer appear to have been caused by acid rain and tsunamis, both of which are by-products of volcanic activity. 

Soils derived from basic volcanic ejecta, metamorphic rocks and granitic rocks have corresponding mineralogies. 

Many rock types have a layered structure, individual rock layers varying in thickness from a few centimeters to tens of meters. Layered rocks include marine sediments, most continental sediments, lava flows and volcanic ejecta, and intrusive sills. The hydraulic properties vary from one rock layer to another, often resulting in abrupt changes along the vertical axis. In terms of the permeability coefficient (k) the lateral coefficient (kx) may significantly differ from the vertical coefficient (kz). The alternation of aquifers and aquicludes results from the layered structure of different rocks, and the occurrence of springs is often controlled by the layering of rocks. Fissures may be restricted to individual rock layers or cross several rock beds, in which case water flow is improved, mainly in the vertical direction. 

Andisols Modified from Ando From volcanic ejecta, dominated by alophane or humic complexes... 

The Byrd-Station ice core was drilled through the West Antarctic ice sheet in 1968 and reached bedrock at a depth of 2,164 m (Gow et al. 1968). This core contains about 2,000 layers of volcanic ash or tephra (Gow and Williamson 1971 Gow 1971). The term includes all volcanic ejecta regardless of the diameters of the particles. These tephra were subsequently described by Kyle and Jezek (1978), Gow et al. (1979), and Kyle et al. (1981). In addition, Epstein et al. (1970) and Johnsen et al. (1972) demonstrated by means of the values of the ice that the Byrd-Station core contains a record of the transition from the cold climate of the Wisconsinan ice age to the present Holocene interglacial. 

Bellatreccia, F., Della Ventura, G., Williams, C. T., Lumpkin, G. R., Smith, K. L. Colella, M. 2002. Non-metamict zirconolite polytypes from the feldspathoid-bearing alkali-syeni-tic ejecta of the Vico volcanic Complex (Ladum, Italy). European Journal of Mineralogy, 14, 809-820. 

Volcanic rocks in Campania and Pontine Islands range from mafic to felsic and mostly have silica undersaturated potassic to ultrapotassic compositions (Fig. 6.2). Mafic rocks with K2O contents close to calc-alkaline basalts have been found both as lavas and as lithic ejecta at Ventotene and Procida-Vivara. Pliocene (about 4.5 Ma) calc-alkaline rhyolites occur at Ponza, and 2 Ma old calc-alkaline basalts to andesites have been found by borehole drilling beneath the Campanian Plain north of Campi Flegrei. 

The volcanoes in the Campania Province, Pontine Islands and Vulture are composed of a wide variety of magma types. Silica undersaturated ultrapo-tassic volcanism is restricted to Somma-Vesuvio, whereas mildly undersaturated to oversaturated potassic rocks occur at Campi Flegrei, Ischia, Procida and Ventotene. In the latter two islands, low potassium compositions close to calc-alkaline basalts are found among lavas and lithic ejecta. Pliocene calc-alkaline rocks are found as rhyolites at Ponza and as basalts and basaltic andesites beneath the Campanian Plain. At Vulture, volcanism is highly enriched in both Na and K, a composition that is distinct from any other volcano in the Italian peninsula. 

The Sicily Province consists of tholeiitic to Na-alkaline magmas. Most rocks are mafic in composition, ranging from basalt to hawaiite and nephelinite, except at Pantelleria where peralkaline acid volcanics (pantellerites) dominate. A few trachytic rocks occur at Etna, Ustica and as lithic ejecta at Linosa. 

Della Ventura G, William CT, Cabella R, Oberti R, Caprilli E, Bellatreccia F (1999) Britholite-hellandite intergrowths and associated REE-minerals from the alkali syenitic ejecta of the Vico volcanic complex (Latium, Italy) petrological implications bearing on REE mobility in volcanic systems. Eur J Mineral 11 843-854... 

A comparable value of 18 t annually is obtained using Olafsson s (1975) estimate of mercury emissions (7 X 10 g Hg/6 X 10 " g ejecta) for the volcanic eruption at Heimay, Iceland, and an estimate of 6 km (—15 X 10 g) for annual, subaerial lava production (—20% of total annual lava production being subaerial Crisp, 1984 Varekamp, personal communication). 

Volcanic activity designating or pertaining to the phenomena of volcanic eruption the explosive or quiet emission of lava, pyroclastic ejecta, or volcanic gases at the earth s surface, usually from a volcano. Sometimes referred as belonging to mountain-building disturbances. 

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