WARM UP!!!WARM UP!!!

Thursday 1/31/08

Describe a

magma

chamber!

Types of Volcanic Eruptions

Why do volcanoes erupt?

• Magma rises to the surface because it is LESS DENSE than the surrounding rock.

• Gases and magma build up inside the volcano and eventually erupts.

Parts of a Volcano…This diagram is located on pg. 185 in your textbook.

It would be a good idea to use the book to find out the information about each part!

Characteristics of Magma• Temperature:

– Hotter = Less Viscous (thinner)– Cooler = More Viscous (thicker)

• Silica Content:– Low Silica = Less Viscous (thinner)– High Silica = More Viscous (thicker)

The thicker the magma, the more explosive the eruption!

Types of Eruptions

1.Quiet

2.Violent

Quiet Eruptions

• Runny lava oozes from volcano vents

• Ex. Iceland and Hawaii

• Produce two types of lava:– Pahoehoe: FAST and HOT– Aa: SLOW and COOL

Violent Eruptions

• Thick and sticky magma plugs vents like a cork. Pressure builds up and eventually explodes.

• Pieces of lava/rock create a pyroclastic flow of ash, cinders, and bombs.

1. Ash = small pieces2. Cinders = medium pieces3. Bombs = large pieces

Mount St. Helens BEFORE the eruption…(1980)

Mount St. Helens DURING the VIOLENT eruption…

Pyroclastic Flow

Mount St. Helens AFTER the eruption…

Stages of Volcanoes

• Active: Can erupt at any moment

• Dormant: May awaken and become active. There is magma still underneath it.

• Extinct: Unlikely to erupt again. No longer has magma underneath it.