Warmup 11/23/15 Tell me everything you can about what you see here Objective Tonight’s Homework To learn about the parts of a volcano Read section 8A. Do p 174: 2, 3, 4, 8

Volcano Anatomy So what is a volcano? At its simplest, a volcano is any spot in the earth’s crust where molten rock has made its way to the surface. While underground, we call it magma. Once aboveground, we call it lava. But there’s a lot more to volcanoes than this. There are many different kinds of volcanoes as well as many different kinds of materials that can come out of them.

Volcano Anatomy This is a typical stratovolcano. The entire thing is powered by the magma chamber at the bottom. This is a supply of molten rock from the Moho that has constant pressure from below to push magma upwards.

Volcano Anatomy A lot of movies show secret volcano lairs in hollowed magma chambers, but the truth is that the magma chamber of a volcano is usually several miles underground. The inside of a volcano isn’t hollow.

Volcano Anatomy Many magma chambers have offshooting dikes and sills. Dikes are tall, vertical cracks in the crust that can often carry magma upwards. Sills are horizontal cracks between layers that often get filled with magma as well.

Volcano Anatomy

Some dikes and sills can carry magma all the way to the surface. These can create parasitic cones that erupt with lava. These vents are rarely the main volcanic vent, but do relieve some of the pressure.

Volcano Anatomy

At the top of the volcano is the crater. This is the opening into the volcano from which lava flows. When not active, these don’t have a big hole that goes straight into the earth. They usually plug up temporarily.

Volcano Anatomy

Lava isn’t the only thing that comes out of a volcano. Volcanoes also spew out tephra. These are huge clouds of volcanic ash and rocks that rain down over the surrounding area for miles.

Volcano Anatomy Tephra ranges from microscopic dust all the way up to huge boulders.

Volcano Anatomy Tephra is usually what builds the actual volcano up. The picture below shows many layers of tephra from several volcanic eruptions. You can see that over time, these layers build up.

Volcano Anatomy While tephra is cool, we’re all more familiar with the liquid rock that flows from a volcano – lava. There are 3 major types of lava. Pahoehoe is usually fairly runny and flows quickly. As it starts to cool, the skin begins to solidify and it slows down greatly. As it cools, it usually forms ropey twisting shapes.

Volcano Anatomy A’a flows more slowly and usually has gas bubbles trapped within it. As it cools, the gas bubbles pop, making the lava harden into sharp, jagged pieces.

Volcano Anatomy The third kind forms underwater and is called pillow lava. As this underwater lava touches water, it cools very quickly and hardens into blobs. As more lava pushes up, these blobs pile up into weird shapes.

Volcano Anatomy The last kind of emission from a volcano is actually the deadliest. It’s called a pyroclastic flow and is a mixture of hot gasses and ash that rolls down the volcano. This can move up to several hundred miles per hour and be close to 2,000 degrees! Some pyroclastic flows can also be nearly invisible, but made of deadly gasses, silently rolling through a village killing everyone in it with suffocation before anyone realizes it’s coming.

Volcano Anatomy

Exit Question What do we call the ash that comes from a volcano? Ash Nimbus Tephra Pahoehoe Sill Doom