Volcanic EruptionsVolcanic Eruptions

And Their Erupting ContentsAnd Their Erupting Contents

Nonexplosive EruptionsNonexplosive Eruptions

• Most common type of eruption

• Produce relatively calm flows of lava

• Lava can slowly creep or travel up to 60 km/h

Types of lavaTypes of lava

• Aa

• Pahoehoe

• Pillow lava

• Blocky lava

Aa lavaAa lava

• Pours out quickly & forms a brittle crust

• Crust is torn into jagged pieces as lava continues to move beneath it.

• A’a lava flows have a very rough surface because of their high eruption rates.

• Named for the painful experience gained by walking across these jagged pieces if walking barefoot

A’a-LavaA’a-Lava

PahoehoePahoehoe1. 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.

Pahoehoe lava samplingPahoehoe lava sampling

Pillow LavaPillow Lava

1. 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.

Pillow lavaPillow lava3. 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.

Blocky LavaBlocky Lava• Cool stiff lava that does not travel far from

the erupting vent.• It cools and form sharp edged chunks.

Explosive (Pyroclastic) eruptionsExplosive (Pyroclastic) eruptions

• Rarer than nonexplosive eruptions

• Very destructive effects

• Clouds of hot debris, ash, and gas rapidly shoot out of the volcano during an explosive eruption.

• Ash can encircle the globe and stay in the atmosphere for years.

The Cataclysmic 1991 Eruption of Mount Pinatubo, The Cataclysmic 1991 Eruption of Mount Pinatubo, Philippines Philippines

  

The second-largest volcanic eruption of this century, and by The second-largest volcanic eruption of this century, and by far the largest eruption to affect a densely populated area, far the largest eruption to affect a densely populated area, occurred at Mount Pinatubo in the Philippines on June 15, occurred at Mount Pinatubo in the Philippines on June 15,

1991. The eruption produced high-speed avalanches of hot 1991. The eruption produced high-speed avalanches of hot ash and gas, giant mudflows, and a cloud of volcanic ash ash and gas, giant mudflows, and a cloud of volcanic ash

hundreds of miles across. The impacts of the eruptionhundreds of miles across. The impacts of the eruptioncontinue to this day.continue to this day.    

The Cataclysmic 1991 Eruption of The Cataclysmic 1991 Eruption of Mount Pinatubo, PhilippinesMount Pinatubo, Philippines

A huge cloud of volcanic ash and gas rises above Mount Pinatubo, Philippines, on June 12, 1991. Three days later, the volcano exploded in the second-largest volcanic eruption on Earth in this century. Timely forecasts of this eruption by scientists from the Philippine Institute of Volcanology and Seismology and the U.S. Geological Survey enabled people living near the volcano to evacuate to safer distances, saving at least 5,000 lives.

Pyroclastic (Explosive) EruptionsPyroclastic (Explosive) Eruptions

4 types of pyroclastic material:1. Volcanic blocks

2. Volcanic bombs

3. Lapilli

4. Volcanic Ash

Volcanic BlocksVolcanic Blocks1. 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.

Volcanic BombsVolcanic 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.

LapilliLapilli

1. Lapilli means “little stones” in Italian.

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

Volcanic AshVolcanic Ash

1. 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.

Review1. 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. Blocks8. Lapilli9. Bombs10. Ash