Editing Seamount (section)

===Geochemistry and evolution===
[[File:Submarine Eruption-numbers.svg|thumb|right|Diagram of a submarine eruption (key: 1. [[Water vapor|Water vapor cloud]] 2. Water  3. [[Stratum]] 4. [[Lava|Lava flow]] 5. [[Magma conduit]] 6. [[Magma chamber]] 7. [[Dike (geology)|Dike]] 8. [[Pillow lava]]) [[:File:Submarine Eruption-numbers.svg|Click to enlarge]]]]

Most seamounts are built by one of two volcanic processes, although some, such as the [[Christmas Island Seamount Province]] near Australia, are more enigmatic.<ref name=naturegeo>{{cite journal|author1=K. Hoernle |author2=F. Hauff |author3=R. Werner |author4=P. van den Bogaard |author5=A. D. Gibbons |author6=S. Conrad |author7=R. D. Müller |name-list-style=amp |title=Origin of Indian Ocean Seamount Province by shallow recycling of continental lithosphere|journal=[[Nature Geoscience]]|date=27 November 2011|volume=4|issue=12 |pages=883–887|doi=10.1038/ngeo1331|bibcode = 2011NatGe...4..883H |citeseerx=10.1.1.656.2778}}</ref> Volcanoes near [[Divergent boundary|plate boundaries]] and [[mid-ocean ridge]]s are built by [[Igneous rock#Decompression|decompression melting]] of rock in the [[upper mantle (Earth)|upper mantle]]. The lower density [[magma]] rises through the crust to the surface. Volcanoes formed near or above [[Subduction|subducting zones]] are created because the subducting [[tectonic plate]] adds [[Volatile (astrogeology)#Igneous petrology|volatiles]] to the overriding plate that lowers its [[melting point]]. Which of these two process involved in the formation of a seamount has a profound effect on its eruptive materials. Lava flows from mid-ocean ridge and plate boundary seamounts are mostly [[basalt]]ic (both [[Tholeiitic basalt|tholeiitic]] and [[Igneous rock#Chemical classification|alkalic]]), whereas flows from subducting ridge volcanoes are mostly [[calc-alkaline]] lavas. Compared to mid-ocean ridge seamounts, subduction zone seamounts generally have more [[sodium]], [[alkali]], and volatile abundances, and less [[magnesium]], resulting in more explosive, [[viscous]] eruptions.<ref name=oceanography-geo/>

All volcanic seamounts follow a particular pattern of growth, activity, subsidence and eventual extinction. The first stage of a seamount's evolution is its early activity, building its flanks and core up from the sea floor. This is followed by a period of intense volcanism, during which the new volcano erupts almost all (e.g. 98%) of its total magmatic volume. The seamount may even grow above sea level to become an [[oceanic island]] (for example, the [[2009 Tonga undersea volcanic eruption|2009 eruption]] of [[Hunga Tonga]]). After a period of explosive activity near the [[sea level|ocean surface]], the eruptions slowly die away. With eruptions becoming infrequent and the seamount losing its ability to maintain itself, the volcano starts to [[Erosion#Water|erode]]. After finally becoming [[Volcano#Extinct|extinct]] (possibly after a brief rejuvenated period), they are ground back down by the waves. Seamounts are built in a far more dynamic oceanic setting than their land counterparts, resulting in horizontal subsidence as the seamount moves with the tectonic plate  towards a [[subduction zone]]. Here it is subducted under the plate margin and ultimately destroyed, but it may leave evidence of its passage by carving an indentation into the opposing wall of the subduction trench. The majority of seamounts have already completed their eruptive cycle, so access to early flows by researchers is limited by late volcanic activity.<ref name=oceanography-geo>{{cite journal|author1=Hubert Straudigal |author2=David A Clauge |name-list-style=amp |title=The Geological History of Deep-Sea Volcanoes: Biosphere, Hydrosphere, and Lithosphere Interactions |journal=[[Oceanography (journal)|Oceanography]] |volume=32 |series=Seamounts Special Issue |issue=1 |url=http://www.tos.org/oceanography/issues/issue_archive/issue_pdfs/23_1/23-1_staudigel2.pdf |access-date=25 July 2010 |url-status=dead |archive-url=https://web.archive.org/web/20100613141518/http://www.tos.org/oceanography/issues/issue_archive/issue_pdfs/23_1/23-1_staudigel2.pdf |archive-date=13 June 2010}}</ref>

Ocean-ridge volcanoes in particular have been observed to follow a certain pattern in terms of eruptive activity, first observed with [[Hawaiian - Emperor seamount chain|Hawaiian seamounts]] but now shown to be the process followed by all seamounts of the ocean-ridge type. During the first stage the volcano erupts basalt of various types, caused by various degrees of [[Mantle (geology)#Movement|mantle melting]]. In the second, most active stage of its life, ocean-ridge volcanoes erupt tholeiitic to mildly alkalic basalt as a result of a larger area melting in the mantle. This is finally capped by alkalic flows late in its eruptive history, as the link between the seamount and its source of volcanism is cut by crustal movement. Some seamounts also experience a brief "rejuvenated" period after a hiatus of 1.5 to 10 million years, the flows of which are highly alkalic and produce many [[xenolith]]s.<ref name=oceanography-geo/>

In recent years, geologists have confirmed that a number of seamounts are active undersea volcanoes; two examples are [[Kamaʻehuakanaloa Seamount|Kamaʻehuakanaloa]] (formerly Lo‘ihi) in the [[Hawaiian Islands]] and [[Vailulu'u]] in the [[Manua|Manu'a Group]] ([[Samoa]]).<ref name=agu/>