CASE STUDY - Hunga Tonga volcano

Question 1

Where is the Hunga Tonga volcano located?

Answer 1

Along the destructive plate boundary where the oceanic Pacific plate subducts beneath the less dense Indo-Australian plate.

Question 2

How can the tectonic setting of the Hunga Tonga volcano be described?

Answer 2

The volcano is formed along a destructive plate boundary where there is an oceanic-oceanic collision zone in the Kermadec-Tonga Ridge. This forms a long volcano and island chain.

Question 3

What is the nature of the Hunga Tonga explosion (what occured) ?

Answer 3

• 7.1 km of magma ejected
• local tsunami was 18-20m high
• triggered 400,000 lightning bolts (record number)
• pyroclastic flows up to 700km/hr

Question 4

Why was the tsunami so large?

Answer 4

• 700m collapse of the caldera generated a large force pushing the water
• high density of the pyroclastic flows through the water.

Question 5

Where was the tsunami recorded?

Answer 5

In the Pacific, Atlantic and Meditteranean seas.

Question 6

Why was the Hunga Tonga volcano so explosive?

Answer 6

The 200m deep caldera was the sweet spot for a violent eruption to occur since:
- not deep enough for the water pressure above to allow an insulating film of steam to form
- deep enough to allow the water to increase the explosivity since the collision of the magma and with the water caused it to expand by 70%. This caused a reaction which tore the new magma apart, causing a chain reaction to occur.

Question 7

What were the social impacts of the Hunga Tonga eruption?

Answer 7

• 4 people died in Tonga (85% affected)
• the undersea communications cable was severed (no access to remittances upon which 40% of the population were reliant)
• water tanks in Nuku’alofa contaminated with ash so became unsafe to drink

Question 8

What were the economic impacts of the Hunga Tonga eruption?

Answer 8

• $90.4 million in damages (18.5% of Tonga’s gross GDP)
• 85% of agriculture impacted, main industry
• $5 million a year lost due to damage to tourist attractions

Question 9

What were the environmental impacts of the Hunga Tonga eruption?

Answer 9

• Beaches unsafe to swim in due to toxins released by the volcanic ash
• Ash smothered some coral reef.

Question 10

What was the dominant political impact of the Hunga Tonga eruption?

Answer 10

COVID 19 was transmitted to Tongan populations through the provision of aid relief.

Question 11

What were the immediate responses to the Hunga Tonga eruption?

Answer 11

• Volcanic activity alert given (14th Jan)
• Planes of foreign aid arrived within 5 days to clear the port runway
• Tongan navy evacuated 62 inhabitants.

Question 12

What were the long-term responses to the Hunga Tonga eruption?

Answer 12

• Matattoa Island is being built which can withstand a category 4 cyclone
• The Tonga Eruption Seabed Mapping Project has started to build a map (mitigation and adaptation can be planned for quicker)

Question 13

Give some examples of global responses to the Hunga Tonga eruption to show how globalisation has changed hazard responses.

Answer 13

1. Australia: deployed two navy ships to provide support
2. UK: 90 family tents, 6 community tents, wheelbarrows
3. USA: $20 million donated 6 months after the eruption
4. World Bank: $8 million in emergency funding donated.