Types of Eruptions:Types of Eruptions:Explosive and NonexplosiveExplosive and Nonexplosive

Chapter 9Chapter 9

A. Types of LavaA. Types of Lava

• There are 4 main types of lava:

1. A’a

2. Pahoehoe

3. Pillow

4. Blocky

B. A’a-LavaB. A’a-Lava1. A’a lava flows have a very rough,

rubbly surface because of their high eruption rates.

As the upper surface of the lava cools and becomes rock, it is continually ripped apart by the moving molten lava inside the flow.

2. Pieces of the rocky surface are broken, rolled and tumbled along as the lava flow moves. When finally cooled to a solid, a’a lava flows look like a jagged heap of loose rock that is very difficult to walk over without stumbling and getting cut.

C. PahoehoeC. Pahoehoe1. Pahoehoe lava flows have a

relatively smooth surface texture because of their low eruption rates.

2. Pahoehoe lava flows develop surface crusts that form thick plates with ropy and/or gently undulating surfaces.

D. Pillow LavaD. Pillow Lava1. Pillow lava forms from

underwater eruptions

2. “Pillow” lava is so-called because it forms rounded lumps that look like fat pillows, or the bolster cushions of a sofa.

3. The pillows can form piles a few to tens of meters high.

4. Pillow lava flows can be many hundreds of meters to kilometers long.

E. Blocky LavaE. Blocky Lava1. Cool stiff lava that does not travel far from

the erupting vent.

2. It cools and form sharp edged chunks.

F. Pyroclastic Material from F. Pyroclastic Material from EXPLOSIVE ERUPTIONSEXPLOSIVE ERUPTIONS

1. 4 types of pyroclastic material

a. Volcanic blocks

b. Volcanic bombs

c. Lapilli

d. Volcanic Ash

G. Volcanic BlocksG. Volcanic Blocks

1. Volcanic blocks are solidified rock fragments greater than 64 mm in diameter.

2. Blocks commonly are ejected during explosive eruptions and consist of older pieces of the volcano.

H. Volcanic BombsH. Volcanic Bombs

1.Volcanic bombs are large pieces of magma that harden in the air as the erupt out of a volcano.

2.They can form in a variety of sizes and shapes.

I. LapilliI. Lapilli 1.Lapilli means “little stones” in Italian.

2.They are tiny pieces of magma that harden before they hit the ground.

J. Volcanic AshJ. Volcanic Ash1.Volcanic ash

forms when gases in stiff magma expand rapidly.

2.The walls of the gas bubbles explode into tiny glasslike slivers.

3.Ash makes up most of a pyroclastic eruption.

ReviewReview

1. List the 4 types of lava.2. This type of lava is very rough with jagged edges.3. This type of lava forms from underwater eruptions, looks like

rounded lumps.4. This type of lava has a smooth surface and rounded edges.5. This type of lava forms sharp edged chunks.6. List the four types of pyroclastic material.7. These are large blobs of magma that have cooled and hardened

as they flew through the air.8. These are tiny pieces of magma that have hardened in the air.9. These are solid rock fragments and usually consist of pieces of

the old volcano.10. This is formed from when gases in stiff magma expand and

explode into slivers.

AnswersAnswers

1. A’a, pahoehoe, pillow, blocky2. A’a3. Pillow4. Pahoehoe5. Blocky6. Blocks, bombs, lapilli, ash7. Bombs8. Lapilli9. Blocks10. Ash