Volcanic Eruptions

Describe the types of pyroclastic materials and lava flows

Volcanic EruptionsDescribe the types of pyroclastic materials and lava flows
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The fragments of rocks that form during an eruption

Pyroclastic material is simply the material that forms and is expelled during a volcanic eruption. This material is expelled because of the viscosity of the felsic lava which traps gases such as carbon dioxide and water vapor. This causes an explosive eruption which results in pyroclastic material being ejected.

Classified Felsic Pyroclastic Material

Like everything else, scientists love to classify so naturally, the pyroclastic material erupting from the volcano is classified according to the sizes of the material. There are five basic types: volcanic ash, volcanic dust, lapilli, volcanic bombs and volcanic blocks.
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Volcanic Ash and Dust

Volcanic ash is pyroclastic material that are less than 2 mm in diameter and volcanic dust is less than 0.25 mm. There isn't much difference between volcanic ash and dust except the size of the particles.

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Lapilli

Lapilli is pyroclastic material that is less than 64 mm in diamter. Lapilli is a latin word that means "little stones". The description of the lava matches its name quite well.

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Volcanic Bombs and Blocks

Volcanic bombs are large chunks of pyroclastic material that are hurled through the air hot, and as it cools in the air it forms a spindle shape. Volcanic bombs are large pieces of solid rock blasted from the volcano during an eruption.

Dome collapse and pyroclastic flow at Unzen Volcano
Pyroclastic Flow Unzen Volcano Kyushu, Japan. This pyroclastic flow killed 41 people.

Classified Mafic Lava Types

There are three basic types of mafic lava flows. These lava flows are pahoehoe, aa, and blocky lava. Pahoehoe is mafic lava that takes the shape of a rope. The word pahoehoe means "ropy" in Hawaiian. As it cools it forms a smooth, ropy texture. The second type of lava is aa. Aa is also a mafic lava. This lava forms as the crust deforms rapidly or grows too thick to form wrinkles, and instead breaks off into jagged chunks. The third type of lava is blocky lava. Blocky lava is also a mafic lava. This lava is very viscous and it causes it to break off into large chunks near the vent of the volcano.

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Pahoehoe Lava

Smooth, ropy texture and least viscous.

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Aa Lava

Broken, jagged edges and more viscious than pahoehoe.

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Blocky Lava

Large, sharp chunks and the most viscous.

Lava Flow at Volcano

Volcan en erupcion. Maravillas de la naturaleza.

Three Types of Volcanoes

Describe the three different types of volcanoes

Volcanoes are classified into three different types which are based on the volcanoe's cone. The shape of the volcano cone is dependent on the viscosity of the mafic magma and the viscosity of the felsic pyroclastic material. This material builds up along the main vent of the volcano. The funnel at the top of volcano is known as the crater, which forms from the volcanoe's eruptions. The three different types of volcanoes are shield volcano, cinder cone volcano, and composite volcano.

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Mauna Loa, Shield

Mauna Loa is a shield volcano in Hawaii. Hawaii is a hot spot which was created by a mantle plume. Mauna Loa is a shield volcano with the following chracteristics. The volcano covers a wide area, it is broad at the base and forms quiet eruptions. The mafic lava flows out around the vent, hardens, and builds up a cone. The mafic lava is made up of magnesium and iron, and it is dark in color and has low viscosity.

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El Paricutin, Cinder Cone

El Paricutin is a famous cinder cone volcano located in Mexico. El Paricutin is a cinder cone volcano which has the characterisitic of having very steep slopes and having very explosive eruptions of pyroclastic material such as volcanic ash, dust, lapilli, volcanic boms and blocks. THey pyroclastic material usually made up of felsic lava which contains silica and feldspar, and is light in color.

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Mt Fuji, Composite

Mt. Fuji is a composite volcano located in the Pacific Ring of Fire in Japan. This composite volcano has the characteristics of being made up of both mafic lava layers and felsic pyroclastic materials. These layers are alternating in the volcano. During a quiet eruption the lava flows down the sides of the volcano and hardens. During a more violent eruption, the pryroclastic material is expelled and it forms a pyroclastic layer on top of the lava layer. Over time, they have alternating layers. They are also called stratovolcanoes. "Strato" means layered.

Calderas form in two ways

A caldera is a large, ciruclar depression that forms when the magma chamber below a volcano partially empties and causes the ground above to sink.
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Emptying of Magma Chamber

One way a caldera forms is when the volcano erupts and empties the magma chamber. Once the magma chamber is empty, the volcanic cone can collapse inward forming a caldera.

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Powerful Eruption

If a volcano erupts with large amounts of magma, it can also cause a caldera to form.

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Calderas May Fill with Water

Crater Lake, Mount Mazama in Oregon

Identify four signals of an eminent volcano eruption

1. Changes in earthquake activity.

2. Temperature changes within the rock

3. Surface bulges

4. Changes in the amount and composition of gases