Lecture 1 - Volcanic Hazards

Question 1

Pyroclasts

Answer 1

All solid fragments ejected from volcanoes

Question 2

Tephra

Answer 2

All pyroclasts that fall to the ground from eruption columns.

Question 3

Monogenetic and Polygenetic

Answer 3

Volcanoes that erupt once and volcanoes that erupt many times

Question 4

What forms explosive eruptions?

Answer 4

Large amounts of entrapped gases and high visocsity magma

Question 5

What forms effusive eruptions?

Answer 5

Small amounts of entrapped gases and low viscosity magma

Question 6

Why do we have volcanoes?

Answer 6

Primordial heat and radioactive decay of K, U and Th

Question 7

Volcanism at divergent plate boundaries

Answer 7

• Along mid-ocean ridges
• 75% of annual output of magma on Earth

Question 8

Volcanism at hotspots

Answer 8

Characteristics: Shallow slopes, Shield volcanoes
- Usually non-explosive
- Mostly basaltic lava flows

Question 9

Iceland: Where hotspot and MOR meet

Answer 9

-Large volumes
- Low viscosity
- Hot 1200
- Fissure volcano type and usually non-explosive

Question 10

Viscosity

Answer 10

High viscosity - slow-moving
Low viscosity - Fast moving

Question 11

Basaltic Lava

Answer 11

• Most common rock type in the curst 2/3 surface
• Low silica content so low viscosity

Question 12

A a lava

Answer 12

Eruption Temperature - 1000 - 1100°c
Rough lava

Question 13

Pahoehoe Lava

Answer 13

Eruption Temperature - 1100 - 1200°c
Smooth lava with rolls

Question 14

Characteristics of shield volcanoes

Answer 14

Low viscosity
Low silica magma
Gentle sloping flanks

Question 15

Volcanic Explosivity Index

Answer 15

Describes the intensity of a volcanic eruption
An increase in number represents an increase around a factor of 10