Volcano Web /

Introduction

A volcano is a location where magma, or hot melted rock from within a planet, reaches the surface. It may happen violently, in a massive supersonic explosion, or more quietly, as a sticky, slow lava flow.

Volcanoes have been a part of earth's history long before humans. Compare the history of human beings, a few million years in the making, to that of the Earth, over four billion years in the making. Volcanoes were important contributors to the early earth atmosphere by releasing gases such as nitrogen (N2), carbon dioxide (CO2), and ammonia (NH4).

Volumes of Some Well-Known Volcanic Eruptions

VOLCANO Eruption Date Volume in km3
eruptions
observed
by humans		 Paricutin, Mexico 1943 1.3
Mount St.Helens,
Washington		 1980 4
Mt. Vesuvius, Italy 79 A.D. 4
Karakatoa, Indonezia 1883 18
inferred
by study
of depozits		 Long Valley, California pre-historic > 450 & 700
Yellowstone, Wyoming pre-historic 400

Note that volcanic eruptions that occurred before historic times were several orders of magnitude larger (more than 1000 km3 in erupted volume) than ones observed by humans.

Volcanic Rocks

 Scientists study rocks at many different scales.

Pumice is one kind of rock formed by volcanic eruptions picture of pumice that are very explosive. Hot, frothy volcanic magma quickly cools, leaving a structure of many twisted air holes inside. Pumice is thus very light weight.

If you move your mouse over the image, you can see how pumice looks under the microscope.

A thin section is a layer of the rock cut so thin that the light from a microscope shines through, allowing us to see the structure of the rock.

The twisted chambers here represent the air pockets preserved inside the rock when this rock blew out of a volcano.