Volcanic Hazards

Question 1

Vulcanicity

Answer 1

Vulcanicity refers to all volcanic activities related to magma being forced into the crust.

Question 2

Volcanoes

Answer 2

Volcanoes are openings in the Earth’s crust through which lava, ash and gases erupt. They mark the presence of magma within the Earth’s crust.

Question 3

Magma

Answer 3

Molten rock beneath the surface is referred to as magma, but once it is ejected at the surface it is called lava.

Question 4

Where do volcanic hazards occur

Answer 4

Mostly near constructive and destructive plate margins

Question 5

Effect of constructive margins on volcanic eruptions and landforms

Answer 5

Basaltic lava
Runny, less viscous, low in silica
Regular and continuous eruption
Mainly lava
Volcano type: Lava plateau, shield volcano, lava

Question 6

Effect of destructive margin on volcanic eruption and landform

Answer 6

Andesitic lava
Slow flowing, viscous, high in silica
Long dormant periods: less frequent
Tephra, pyroclastic flow, ash, gases
Volcano type: acid lava dome, composite cone, layers of ash and lava

Question 7

Lava flow

Answer 7

Lava can flow from volcanic vent down the side of a volcano
Speed and distance travelled depends on viscosity, temperature and slope steepness:
Basaltic, low viscosity, low silica, high temp can flow some distance before solidifying
Acidic, high viscosity, high silica, low temp flows slower and may solidify in vent - results in explosive unpredictable eruptions.

Most relatively slow - people can evacuate
Destroys anything in its path - burning, knocking down, burying

Question 8

Pyroclastic flow

Answer 8

A mix of ash, gases, lava and hot rock rising from eruption and moves at rapid speeds (up to 80km/h) and flows a long way.

Travel fast and happen with little warning so can cause widespread destruction and death.

Common in eruptions of acidic lava at subduction zones.

Question 9

Tephra

Answer 9

Solid rock fragments ejected during volcanic eruptions

Question 10

Volcanic gases

Answer 10

Lava contains gases such as c02 and sulfur dioxide which are released into atmosphere during eruption.
Highly dangerous - if breathed in

Question 11

Nuées ardentes

Answer 11

Means ‘glowing cloud’ and is a dense, rapidly moving cloud of hot gases, ashes and lava fragments from a volcanic eruption. It is a type of pyroclastic flow that contains more dense material and so doesn’t travel as far.

Question 12

Ash fallout

Answer 12

Ash can be ejected high into the atmosphere and, depending on prevailing winds, can cover a large area
Range of sizes - larger, heavier particles deposited near volcano and lighter further away

Question 13

Mudflows (Lahars)

Answer 13

Lahars are destructive mudflows formed when ash and other volcanic material are mixed with water. They flow at speeds of up to 60km/h and are highly erosive.

Question 14

Acid rain

Answer 14

Volcanic gases can react with water vapour in atmosphere and then fall as acid rain
Can damage ecosystems

Question 15

What is magnitude ?

Answer 15

Volcanic events range from small, slow lava to huge eruptions. Magnitude can be measured using Volcanic Explosivity Index, which grades volcanoes on a scale based on amount of material ejected and how high it is blasted.

Question 16

What is frequency?

Answer 16

Some active volcanoes erupt once every 100,000 years or so, whereas others every few months. Generally less frequent eruptions are larger in magnitude and more damaging.

Question 17

What is randomness vs regularity?

Answer 17

Some volcanoes erupt at very regular intervals, whereas some may be dormant for thousands of years and then erupt several times in quick succession.

Question 18

What is predictability?

Answer 18

The regularity with which a volcano erupts can help scientists to predict when it might erupt again. They also monitor tiny earthquakes and changes in shape of volcano which suggests an eruption is imminent.

Question 19

Give a place example for lava flow

Answer 19

Cape Verde - 75% of buildings destroyed

Question 20

Give place example for pyroclastic flow

Answer 20

Mount Vesuvius, Pomepii

Question 21

Give place example for Nuées ardentes

Answer 21

Martinque - Killed 30000

Question 22

Give place example for tephra and ash fall out

Answer 22

Eyjaffjallajökull (Iceland) - 100,000 flights cancelled

Question 23

Give place example for volcanic gases

Answer 23

Lake Nios in area of Northern Cameroon - 1,200 killed

Question 24

Give place example for mudflows

Answer 24

Amero - deadliest Lahar recorded in history, 25,000 deaths

Question 25

Give place example for acid rain

Answer 25

Tonga (2022)

Question 26

What are the factors which lead to the formation of
mudflows, a volcanic hazard?

Answer 26

Associated with rapid melting of ice/snow following a volcanic eruption.
Occur where there is a substantial amount of ice or snow at high altitude
Debri is comprised of Pyroclastic flow, volcanic ash, rocks, water. It will typically flow down valley side and speed is affected by steepness of slope and gravity.