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Seeing In The Dark

In the movies, there are all sorts of nasty things that can see perfectly well in the dark. More realistic movies also boast their share of 'beasts' that can see in the dark. Who could forget the eerie sight of FBI trainee Clarice Starling being stalked in the pitch-dark basement of the psychotic killer's torture house? The insecurity and near ...

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SeeingInTheDark
Physics

Earth's Magnetism

Most ancient civilizations were aware of the magnetic phenomenon. Sailors in the late thirteenth century used magnetized needles floating in water as primitive compasses to find their way on the sea. ... Continue reading

EarthsMagnetism
Geology

Flipping Magnetic Fields

North and south. We take these directions for granted. Pull out a compass and the needle will swing to the north in response to the magnetism in the Earth's crust. The magnetic poles roughly coincide ... Continue reading

FlippingMagneticFields
Biology

Wetlands Top Ecosystem

Wetlands are areas where water covers the soil, or is present either at or near the surface of the soil all year or for varying periods of time during the year, including during the growing season. ... Continue reading

Wetlands
Astronomy

Hats Off to the Sombrero

This nearly edge-on view of the Sombrero galaxy shows that the disks of spiral galaxies are incredibly thin. The majestic spiral arms cannot be seen in this side view of the Sombrero, named because it ... Continue reading

HatsOfftotheSombrero

What is Volcanic Ash?

VolcanicAshSmall jagged pieces of rocks, minerals, and volcanic glass the size of sand and silt (less than 1/12 inch or 2 millimeters in diameter) erupted by a volcano are called volcanic ash. Very small ash particles can be less than 1/25,000th of an inch (0.001 millimeter) across. Though called 'ash,' volcanic ash is not the product of combustion, like the soft fluffy material created by burning wood, leaves, or paper. Volcanic ash is hard, does not dissolve in water, is extremely abrasive and mildly corrosive, and conducts electricity when wet.

Volcanic ash is formed during explosive volcanic eruptions. Explosive eruptions occur when gases dissolved in molten rock (magma) expand and escape violently into the air, and also when water is heated by magma and abruptly flashes into steam. The force of the escaping gas violently shatters solid rocks. Expanding gas also shreds magma and blasts it into the air, where it solidifies into fragments of volcanic rock and glass.

Once in the air, hot ash and gas rise quickly to form a towering eruption column, often more than 30,000 feet, (9144 m) high. Larger rock fragments more than 2 inches, (5 cm) across ejected by the explosion typically fall within a few miles of the eruption site. However, wind can quickly blow fine ash away from the volcano to form an eruption cloud. As the cloud drifts downwind from the erupting volcano, the ash that falls from the cloud typically becomes smaller in size and forms a thinner layer. Ash clouds can travel thousands of miles, and some even circle the Earth.