The composition of the gases in magma are:

• Mostly H2O (water vapor) & some CO2 (carbon dioxide)

• Minor amounts of Sulfur, Chlorine, and Fluorine gases.

Gas (mainly water vapor) dissolved in magma tends to increase its ability to flow. Therefore, in near-surface environments, the loss of gases makes magma more viscous.

pahoehoe refers to lava with a smooth, shiny, or swirled surface and comes from the Hawaiian verb hoe, "to paddle" (since paddles make swirls in the water)

`a`a refers to lava having a rough surface and comes from the Hawaiian word meaning "to burn.”

The stark contrast in basalt flow types is seen here of a `a`a flow that advanced over the smoother ropey-surface of an older pahoehoe flow.

Shapes and relative sizes of volcanoes

Olympus Mons. Mars, is 624 km in diameter, 25 km high, and is rimmed by a 6 km high scarp.

flood basalts

Kilimanjaro

Cinder cone

La Poruna cinder cone in northern Chile is 300 m high.

Pinatubo June 1991

pyroclastic flow

Mt Rainier

welded tuff

Last tephra eruption occurred about 2,200 years ago

Cascades

Cascades

Valles Caldera, New Mexico.

Devil’s tower, Wyoming

Shiprock. New Mexico

SHIPROCK

This huge volcanic neck was formed in Pleistocene time (sic), over 3,000,000 years ago. It rises 1700 feet above the surrounding plain and is famed in the legends of the Navajo as "Tsé Bit'a'í" (the rock with the wings). They hold that it was the great bird that brought them from the north.

Shiprock is composed of fractured volcanic breccia and black dikes of igneous rock called "minette". It is the erosional remnant of the throat of a volcano, and the volcanic breccia formed in a diatreme. The exposed rock probably was originally formed 2,500-3000 feet (750-1,000 meters) below the earth's surface, but it was exposed after millions of years of erosion. Wall-like sheets of minette, known as dikes, radiate away from the central formation. Radiometric age determinations of the minette establish that these volcanic rocks solidified about 27 million years ago. Shiprock is in the northeastern part of the Navajo Volcanic Field; the field includes intrusions and flows of minette and other unusual igneous rocks that formed about 25 million years ago. Agathla, also called El Capitan, is another prominent volcanic neck of this field.

http://www.kellymoore.net/shiprock.html

A small volcanic neck near Cerro Castellan. This small neck has been erroneously identified by some as a petrified tree. The "grain" was formed by flow structure in the lava as it ascended; the "knothole" once held a boulder. The white rock is hard volcanic ash and the dark rocks in the background are lava.

Cross-section of Newark Basin

The Palasades is a natural cross section of a diabase sill on the west side of the Hudson River valley across from N. Y. City.

The 3 Watchung Mountains are outcrops of basalt lava flows

Ramopo

Geothermal gradient is the rate of increasing temperature with depth in the Earth. Away from tectonic plate boundaries, it is about 25 °C per km of depth (1 °F per 70 feet of depth) near the surface in most places.

Yosemite, CA

Yellowstone Nat. Park

SCLM = shallow continental lithospheric mantle

migmatite migmatite

migmatite