4.5 - Volcnic Benefits

Question 1

What is causing more people to live near volcanoes?

Answer 1

Increasing global population means more people are living closer to volcanoes

Question 2

What are the benefits of living near volcanoes?

Answer 2

• Fertile soils
• Volcanic ore deposits
• Tourist attractions
• Geothermal resources

Question 3

How do volcanoes benefit soil?

Answer 3

Volcanic soils are fertile and form from the weathering of volcanic rocks and ash.

Fresh volcanic material contains mafic minerals such as olivine and pyroxene which weather easily and release their Mg and Fe, making soil fertile. Layers of ash can act as natural fertilisers, producing increased harvests in years following eruption.

Question 4

How do plants grow in volcanic soil

Answer 4

Although volcanic soil is nutrient rich, it is typically not an ideal environment for plants to grow as its often low in organic matter and can have high levels of heavy metals.

If a plant is able to grow in volcanic soil, it should also contain chlorophyll to carry out photosynthesis.

Chlorophyll is composed of carbon, hydrogen, oxygen and nitrogen, organised around magnesium. Volcanic soil can provide some of the nutrients that are necessary for chlorophyll production.

Question 5

Fertile soil around Naples

Answer 5

There is good soil near the volcanoes in Naples such as Vesuvius. Arable farming elsewhere in the region is much more difficult because limestone forms poor soil

Question 6

How do volcanoes act as ore deposits?

Answer 6

At sea floor vents, magmatic heat drives circulation of seawater and hydrothermal fluid.

These fluids are rich in dissolved metals and precipitate massive sulfide ores.

Question 7

What ores do volcanoes deposit?

Answer 7

VMS = Volcanic massive sulfide ores
- Cu
- Fe
-Zn
-Au
-Ag
Pb

These form around hydrothermal vents (also called black smokers)

Question 8

How does volcanism impact tourism?

Answer 8

It is estimated that more than 100million people visit volcanic sites around the world each year.

• Tourism can be important to local economies such as Nicaragua, South Pacific islands
• There are risks of tourist visits to these volcanoes whether active or even dormant

Question 9

Whakaari/White Island volcanic eruption in 2019

Answer 9

• It is an active andesite strata volcano off the NE coast of NZ
• It had last erupted in 2016 and despite risks it is a popular tourist attraction
• It is a privately owned island but has a monitoring system

On 9th December, 2019, there was a phreatic eruption which is very difficult to predict. 47 people were on the island at the time and 21 of them were killed. 26 suffered severe injuries.

Question 10

What is geothermal energy?

Answer 10

It is energy derived from natural heat of the earth (contained in hot rocks, water, brine or steam)

Question 11

How is a geothermal reservoir formed?

Answer 11

In most volcanic settings, rainwater seeps down into the crust through pores, faults and fractures. It is heated and may rise to the surface to create hot springs and fumaroles or it may be trapped and form a geothermal reservoir.

Question 12

How is renewable energy accelerating?

Answer 12

In 2021, 13% of global primary energy came from renewable technologies. We desperately need to move away from fossil fuels and increase renewable sources to mitigate climate change.

Question 13

Why should we opt for geothermal energy?

Answer 13

With renewable energy, water can be recycled back

• It is clean, plants emit little if any C02 and other harmful gases and particulate matter.
• Unlike wind and sun, geothermal offers continuous power and so is reliable base-load in grid

Question 14

How do we access geothermal heat?

Answer 14

Typical geothermal gradient
- Non volcanic region 25 K km
- Volcanic region 100 K km

• Powder production needs temps over 100 degrees
• We need to drill deep to get this heat, generally over 2-3km

Question 15

Yellowstone supervolcano

Answer 15

It is a hotspot

• Highest temperatures associated with active magmatic systems and zones of rifting (thin crust)
• In most places drilling is needed to access heat

Question 16

What is the equation for heat extraction from a rock?

Answer 16

Heat in rock: Q= p Cp V ‘triangle’ T

Heat = density x heat capacity x volume x change in temperature

Eg. Cooling 1km3 of rock by 100 degrees gives 2.5 x 10(17) J

Question 17

How much energy does a power plant serving major cities usually produce?

Answer 17

Power plants, serving major cities, typically generate 1GW, which is 10(9) J s-1 of energy

In a year 1GW power plant generates 10 (9) J s-1 x 3.1 x 10 (7) s year-1 = 3.1x10 (16) J

• So if this thermal energy were captured and converted into electrical energy- this rock could keep a 1GW power plant going for almost 10 years

Question 18

What is an example of a power plant in Scotland?

Answer 18

Torness nuclear power station, near Edinburgh, 1.2GW

Question 19

How are resources extracted from a geothermal reservoir?

Answer 19

• In active volcanic systems we drill into the geothermal reservoir
• Analogues to oil and gas systems need to have a ‘cap rock’ which seals in the fluid so it cannot rise to the surface
• The cap rock has low permeability and will usually comprise altered clay minerals
• If there are no geothermal fluids (there is hot-dry rock), you can inject water, let it heat up and extract

Question 20

What does the choice of plant depended on?

Answer 20

The type of power plant depends on fluid phases (ie. Steam and/or water) and the temperature

Question 21

What are binary cycle power plants?

Answer 21

Used if the geothermal reservoir temperatures are low (100-150 degrees Celsius)

• They use heat to vaporise organic liquid (eg. Iso -butane, iso- pentane boil at 30 degrees)
• Then this vapour is used to drive turbines
• The turbines cause vapour to condense and this continuously recycles the organic liquid

Question 22

What are the risks and environmental impacts of geothermal plants ?

Answer 22

They are very expensive to build. Drilling 1 well costs $1-5 million.

• There may be vegetation loss and soil erosion
• Slight air heating and local fogging
• Increased noise

Extraction/injection of fluid:
- May impact the water table
- There may be ground subsidence/uplift

Longer term concerns:
- Corrosive or scaling fluids
- Volcanic eruption

Question 23

Where had an example of ground uplift from a geothermal plant?

Answer 23

Staufen, geothermal drilling hit anhydrite which transformed mineral to gypsum and has led to an uplift of 10-30cm

Question 24

Geothermal case study in east africa

Answer 24

Ethiopia, in east africa, has a rapidly growing economy but the power sector is not meeting the demands. This has led to a major impediment to continued growth.

Combined geothermal resources may be vast (over 10GW) but it is yet to be effectively exploited.

Question 25

What is social about Ethiopia?

Answer 25

There is lots of rift volcanism such as fantale volcano and aluto volcano.

• There is lots of steam

Question 26

How to unravel eruptive histories

Answer 26

For most volcanoes eruptive histories are unknown with no monitoring.

We can’t predict exactly when and how these volcanoes might erupt next, but we can make predictions of the probability of an eruption.

Geoscientists are the solution- can calculate the likely ‘recurrence interval’ of an eruption

• Can study the geological record to see how the volcano behaved in the past

Question 27

What are hazard maps?

Answer 27

• Hazard maps are based on topography and volcanic record (magnitude, location, frequency, style of past eruptions)
• Communication between volcano experts, local authorities and government is key to success

Question 28

How can volcanologists monitor volcanoes?

Answer 28

Volcanologists can support communities by providing monitoring infrastructure.

• Networks of seismometers measure earthquakes around active/dormant volcanoes
• Different earthquakes reveal different processes - VT earthquakes represent brittle failure of rock, LF due to cracks resonating as Megan gases move toward the surface

Question 29

How does a seismometer work?

Answer 29

• The magma rises into the magma chamber beneath the volcano
• The rising magma and volcanic gases cause pressure to increase
• A seismometer measures ground vibrations caused by magmatic earthquakes

Question 30

How is ground deformation measured?

Answer 30

Ground deformation can be monitored via GPS stations and tilt meters (on the ground) or by satellite radar

• They can detect magmatic intrusions and magma movement

Question 31

How are gas emissions monitored?

Answer 31

It monitors increase in gas production and change in gas composition. It can also monitor heat flow and changes in water chemistry.

Gas emissions are monitored by satellites (eg. ESA sentinel-5) which can monitor plumes from space

Question 32

What can Geoscientists do overall, instead of telling exactly when an eruption will occur?

Answer 32

• Can make predictions and calculate recurrence interval
• Can create hazard maps
• Monitor the volcano (gas, heat, deformation and seismology)
• Communicate with the authorities and the public (to improve resilience)

Question 33

How can volcanoes be good for climate change?

Answer 33

They emit huge amounts of heat which can be harnessed as geothermal energy.

This energy is clean and ‘free’ and could be used to mitigate climate change.

BUT we need a good understanding of geothermal systems and volcanic hazards before drilling