Lecture 5: Volcanos

Question 1

What are the 3 products of volcanic eruptions?

Answer 1

1. Magma (molten rock)
2. Volatiles (gases)
3. Pyroclasts (airborne material)

Question 2

What are the factors that affect the eruption style, and what do they control?

Answer 2

• composition of the magma
• temperature of the magma
• dissolved gases in the magma

They control the viscosity of the magma

Question 3

What is the magma composition partially related to?

Answer 3

It’s related to the degree of partial melting of asthenosphere rock.

Question 4

What happens with convergent boundaries?

Answer 4

Magma is produced by hydration melting (water driven by subjecting oceanic plate lowers melting point of asthenosphere rock)
- intermediate to felsic magma

Question 5

What are divergent boundaries?

Answer 5

Magma produced by decompression melting (melting of high temperature asthenosphere rock)
- mafic magma

Question 6

What are intrastate hotspots?

Answer 6

Discrete heat plumes that locally melt high temperature asthenosphere rock
- mafic magma

Question 7

What is the main texture of volcanic igneous rocks

Answer 7

Aphanatic (Glassy) texture due to the rapid cooling at Earth’s surface.

Question 8

What are the three most important volcanic rocks?

Answer 8

Basalt (mafic)
Andesite (intermediate)
Rhyolite (felsic)

Question 9

What are the special textures of volcanic rocks?

Answer 9

1. Porphyritic
2. Glassy
3. Vesicular

Question 10

What is a porphyritic texture?

Answer 10

The rock has large crystals (easy to physically see the particles). This was due to slow cooling of magma.

Question 11

What is a glassy texture?

Answer 11

When the magma cools immediately, the crystals do not have time to form.

Question 12

What is vesicular texture?

Answer 12

When the rock has air bubbles within it, the volatiles were trapped in the rock.

Question 13

What makes a volcano more explosive?

Answer 13

Higher volatile content and higher viscosity.

Question 14

What are the 3 types of volcanos?

Answer 14

• shield (small bump, almost looks like flat land)
• composite cone (typical volcano )
• cinder cone (2 bumps)

Question 15

What is a caldera?

Answer 15

When the top of a volcano caves, in it produces a caldera.

Question 16

What are pyroclastic Materials?

Answer 16

Splattered blobs of lava that land as volcanic bombs.

Question 17

Describe a composite cone volcano.

Answer 17

Very large in height and width. Cone shaped.

Intermediate to celtic lava.

Question 18

Describe a cinder cone volcano.

Answer 18

Small with steep slopes, fragments of basaltic cinders and ash are found throughout the volcano.

Question 19

How are calderas produced?

Answer 19

When huge amounts of pyroclastic debris and faces are released through ring fractures surrounding the summit, the crater produced by the pressure of these materials is called a caldera.

Question 20

True or False: Magma’s viscosity is directly related to its silica content.

Answer 20

True: the more silica the magma has, the more viscous it is. Which also makes it more explosive.

Question 21

Why and how is viscosity related to the magnitude of a volcanos eruption?

Answer 21

The more viscous the magma is, the greater its resistance to flow, therefore the greater the eruption.