Volcano Info	EnchantedLearning.com Volcano Dictionary		Volcano Activities and Printouts
	Types of Volcanoes	The Ring of Fire

maar A maar is a shallow, flat-bottomed crater that forms above a diatreme (volcanic vent) when steam explodes. Maars range in size from 200 to 6,500 feet in diameter and from 30 to 650 feet deep. Maars often fill with water and form lakes.

mafic Mafic refers to dark-colored igneous rock or magma that have significant amounts of iron and magnesium. For example, olivine, augite, and hypersthene are mafic rocks.

magma Magma is molten rock (lava) from which igneous rock forms. Magma is be formed from many types of rocks, including basalt, andesite, dacite, and rhyolite

magma chamber A magma chamber is an underground cavity filled with gas-rich magma (molten rock). This magma erupts through volcanoes.

magnetic field The Earth's magnetic field is aligned with the north and south poles, and has reversed many times during geologic history. Sharks may use the magnetic field of the Earth for navigation purposes on migrations.

magnitude The intensity of an earthquake is described by a number in the Richter scale, called the magnitude. The magnitude of an earthquake is calculated from the logarithm of the amplitude of waves recorded by seismographs. A magnitude 2.0 or less earthquake is called a microearthquake and is not felt by people. A magnitude 4.5 or more earthquake can be measured by seismographs all over the world. Tsunamis can be caused by undersea earthquakes of magnitude 7.5 or greater.

mantle The mantle is the layer of the Earth located between the crust and the molten core.

mass extinction Mass extinction is the process in which huge numbers of species die out suddenly. The dinosaurs (and many other species) went extinct during the K-T extinction, which was probably caused by an asteroid colliding with the Earth.

Mesozoic Era The Mesozoic Era ("The Age of Reptiles"), occurred from 245-65 million years ago. It is divided into the Triassic, Jurassic, and Cretaceous periods. Dinosaurs, mammals, and flowering plants evolved during the Mesozoic, and Pangaea broke up. The era ended with the K-T mass extinction.

metamorphic rock Metamorphic rocks are compacted by pressure and heat from deep inside the earth.

meteor A meteor is a meteoroid that has entered the Earth's atmosphere, usually making a fiery trail as it falls. It is sometimes called a shooting star. Most burn up before hitting the Earth.

meteorite A meteorite is a meteor that has fallen to Earth. Meteorites are either stone, iron, or stony-iron.

meteoroid Meteoroids are tiny stones or pieces of metal that travel through space.

1,000,000 million A million is a thousand thousand. The dinosaurs lived millions of years ago.

mineral A mineral is a naturally-occurring solid of definite chemical composition whose atoms usually form a regular pattern.

Miocene epoch The Miocene epoch was a geologic time span that lasted from 24 million to 5 million years ago. During the Miocene, modern birds and many mammals evolved (including the horses, dogs, bears, South American monkeys, and apes in southern Europe). Ramapithecus appeared; this primate was pehaps an ancestor of man. The climate was relatively warm (as compared to the earlier Oligocene or the later Pliocene). There were extensive grasslands (and grasses diversified), and the interior of the continents were relatively dry; northern coniferous forests expanded. Kelp forests appeared in the seas. In North America, the Sierra Nevada Mountains and the Cascade Mountains were formed; in the South America, the Andes Mountains arose. The Bering land bridge formed during the Miocene, connecting Russia and Alaska, allowing many animals to migrat across continents. The Isthmus of Panama also formed during this time. Australia became very dry (but went through wet and dry periods). In Europe, the Mediterranean Sea and Indian Ocean were separated (they had been connected by the Tethys Sea).

Mohorovicic, Andrija Andrija Mohorovicic (1857 - 1936) was a Yugoslavian geophysicist. After examining seismic waves from the 1909 Kulpa Valley earthquake, Mohorovicic theorized that a boundary between the Earth's crust and the upper mantle existed (about 50 km beneath the surface) in which the speed of earthquake waves became very rapid. This region is now called the Mohorovicic discontinuity. A crater on the dark side of the moon was also named for Mohorovicic.

MOHOROVICIC DISCONTINUITY The Mohorovicic discontinuity separates the crust and the upper mantle of the Earth.

monogenetic volcano A monogenetic volcano is one that was formed during a relatively short time period and during a single eruption. Most monogenetic volcanos are basaltic.

Volcano Info	EnchantedLearning.com Volcano		Volcano Activities and Printouts
	Types of Volcanoes	The Ring of Fire

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