The Sept 27, 2014 Phreatic Eruption of Mount Ontake, Japan

Ontake shortly after phreatic eruption on Sept 27.  Photo courtesy EOS.org, 2017

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BATHOLITH…, LOPOLITH…, SILL OR DIKE? – INTRUSIONS (2)

INTRUSIONS PART 2: INTRUSIVE ROCK FORMATIONS

Elephant Rock (NE Lower Austria) is an outcrop of the South Bohemian Pluton (central Europe). This batholith is one of the largest intrusions within the Variscan (or Hercynian) orogeny, with a surface of ~6000 km². The rounded “elephant” shape of the granite blocks is caused by spheroidal or woolsack weathering. (© Isiwal, via Wikipedia)

GRANITE…, SYENITE…, DOLERITE… INTRUSIONS (1)

INTRUSIONS PART 1:  INTRUSIVE IGNEOUS ROCKS

Stone Mountain is a part of the Spruce Pine plutonic suite in North Carolina, U.S.. Petrologically, “the marginal phases are fine- to medium-grained muscovite-biotite tonalite to granodiorite, and the interior of the pluton is largely medium- to coarse-grained leucocratic muscovite-biotite quartz monzonite to granite”. Not that complicated, or is it? (© Nathan Lyons)

Magma is intruded somewhere deep down, it stays down there, it cools down there, never to be seen for the next couple of million years – why should anybody care about it? Well, as we’ll see, in many places it DID come up. In fact, a good percentage of Earth’s surface is made up of intrusive rocks.