Intrusive igneous activity As magma cools underground it

Intrusive igneous activity � As magma cools underground, it will begin to solidify within Earth’s crust. � Once completely crystallized, these masses of igneous intrusive rock are referred to as INTRUSIONS or as PLUTONS � We will talk about several types of igneous plutons: › Dikes, Sills, Laccoliths, Batholiths, & Volcanic Necks

Intrusive igneous activity � Types of intrusive igneous features �Dike – relatively small igneous intrusions formed as magma penetrates into rock fractures and solidifies into thin, sheet-like bodies. �Sill – sheet-like intrusions, like dikes, but they tend to be much thicker, and form as magma intrudes in between layers of sedimentary rock, then cools. Not as common as dikes

Dike

� Diabase dike cutting thru pre. Cambrian age Hakatai Shale at Hance Rapid in the Grand Canyon.

Sill

A sill in the Salt River Canyon, Arizona

Laccolith �Begins as a sill, since material fills in between rock layers. �Because of pressure, some sills can arch up the overlying sediments, creating a mushroom shaped rock body. �Tend to form at shallow depths

Laccolith

Intrusive igneous activity � Intrusive igneous features continued �Batholith �Large plutons lacking a specific shape �Form as huge quantities of magma intrude into country rock, remove fragmets, and melt their way towards the surface. �Most remains underground �Large batholiths can be over 100 miles across

� When batholiths are uplifted and exposed, they are usually resistant strata that form the roots of mountain ranges or eroded highlands.

Batholiths of western North America

Batholith

Intrusive Igneous Activity � Volcanic pipes and necks �Pipes - short conduits that connect a magma chamber to the surface �Volcanic necks (e. g. , Ship Rock, New Mexico) - resistant vents left standing after erosion has removed the volcanic cone

Formation of a volcanic neck

The most famous volcanic neck in the United States is Shiprock, New Mexico

Igneous Intrusions

Volcanoes & Plate Tectonics � Most volcanoes occur in the area known as the Ring of Fire � Volcanoes can form at CONVERGENT & DIVERGENT plate boundaries!! � Volcanoes can also occur within a plate which can result in hot spots and form Island chains like Hawaii & Iceland

� A. Rising mantle plume; B. Rapid decompression melting producing flood basalts; and C. Rising plume tail produced by linear seafloor volcanic chain

Distribution of some of the world’s major volcanoes

Volcanoes and climate � The basic premise �Explosive eruptions emit huge quantities of gases (SO 2) and fine-grained debris �A portion of the incoming solar radiation is reflected and filtered out � Past examples of volcanism affecting climate �Mount Tambora, Indonesia – 1815 �Krakatau, Indonesia – 1883

Volcanoes and climate � Modern examples �Mount St. Helens, Washington - 1980 �El Chichón, Mexico - 1815 �Mount Pinatubo, Phillippines - 1991

Pinatubo Eruption June 1991 � Map showing areal distribution of pyroclastic flows of June 1991 and destructive lahars that ensued in September 1991, killing many more people than the eruption

� Sulfer dioxide emissions of large volcanic eruptions from 1979 -91, in thousands and millions of tons

� Impact of SO 2 emissions on global climate, caused by formation of H 2 SO 4 aerosol, deflecting radiant energy from the Sun into the Stratosphere