Hades Tomography Explorer

Seismic tomography scans have huge potential in the geography classroom. But what are they? In simple terms, they are like a CAT scan of the interior of the Earth.  They are created by measuring the speed of seismic waves. Areas, where there is a low velocity, correspond with hotter, less dense zones in the mantle (e.g. a mantle plume). To find out more about seismic tomography scans take a look at this excellent guide by Earth Scope.

There are a number of tools available to generate seismic tomography scans. Our favourite is the Hades Underworld Explorer. The interface is made to facilitate the discovery and visualisation of mantle anomalies. A tomographic model can be generated by either selecting a section preset or by dragging markers to generate a cross-section of the mantle.

In the example below, a selection has been made in the northwest Pacific, in Asia.

A selection in the north-west Pacific

A selection in the north-west Pacific

The website then generates a tomography scan showing the cross-section of the mantle.

The subduction of the Eurasian plate by the Pacific Plate

The subduction of the Eurasian plate by the Pacific Plate

The depth of the mantle is shown in kilometres on the x-axis. The key shows velocity anomalies. In the case of the tomography scan above the colder, more dense material is shown in blue, while the hotter, less dense material is shown in red. Based on this we can see the destructive margin formed by the Eurasian plate being subducted by the Pacific plate. The Pacific Plate sinking into the mantle as illustrated by the cooler crust (shaded blue), reaches a depth of around 800 km.

In the example below the mantle plume at Hawaii is clearly visible (accessed via the drop-down menu).



Hawaii mantle plume

Hawaii mantle plume

Tomography scans lack the resolution required to image plumes deep within the mantle.

The tomography scan below illustrates the Rift Valley in eastern Africa.

Rift valley transect

Rift valley transect

Rift valley tomography scan

Rift valley tomography scan

The tomography scan below shows the Northern Atlantic.

North Atlantic Transect

North Atlantic Transect

North Atlantic Tomography scan

North Atlantic Tomography scan

In the tomography scan above we can see that the conduit spreads laterally across the North Atlantic, to a depth of around 900 km. There is a conduit feeding this between 900-1200 km along the transect at a depth of around 1000 – 1500 km.

Note: The settings in the Hades Underworld Explorer allow you to customise your tomography scan.

Tomography Scan Settings

Tomography Scan Settings

Alistair Hamill has shared a number of resources on the use of seismic tomography on Twitter and inspired our interest in this area. Below are a selection of tweets by Alistair that are well worth exploring.

Take a look at Alistair’s timeline on Twitter to see how he has used them in his classroom.

If you know of resources to support the use of seismic tomography scans please share them in the comments below.


Tonga Volcano

Please consider donating to the New Zealand Red Cross Pacific Tsunami appeal to support those affected by the recent eruption of the Hunga Tonga-Hunga Ha’apai volcano.

This page continues to be updated as news breaks.

The Hunga Tonga-Hunga Ha’apai volcano

The Hunga Tonga-Hunga Ha’apai volcano is located in the South Pacific, around 65km (40 miles) north of Tonga’s capital, Nuku’alofa. The volcano is part of an arc of volcanic islands known as the Tonga-Kermadec Islands volcanic arc and forms part of the Pacific Ring of Fire.

The location of the Hunga Tonga-Hunga Ha’apai volcano

The location of the Hunga Tonga-Hunga Ha’apai volcano

What was the volcano like before it erupted?

Before its eruption, the Hunga Tonga-Hunga Ha’apai volcano was 1.8km high and 20km wide. However, the volcano was only 114 metres above sea level at its highest point. The video below illustrates the majority of the volcano is undersea (shared by A Hamill).


Volcanic activity in 2009 joined the islands of Hunga Tonga and Hunga Ha’apai, which were themselves produced by older volcanic eruptions.

Hunga-Tonga-Hunga-Ha’apai volcano

The satellite image above was taken before the eruption of the Hunga Tonga-Hunga Ha’apai volcano.

Recent activity of the Hunga Tonga-Hunga Ha’apai volcano

The volcano became active on 20th December 2021. However, it was declared dormant by the Tonga Geological Service on 11th January 2022.

At around 4.20 am local time on 14th January 2022 (3.10 pm GMT on 13th January 2022), the Hunga Tonga-Hunga Ha’apai volcano erupted, sending plumes of ash, steam and gas up to 20km into the atmosphere.

The video below shows the eruption of the Hunga Tonga-Hunga Ha’apai volcano on 14th January 2022.

The images below show the volcano on 7th January 2022 then again after the eruption on the 13th January 2022. The satellite images after the eruption show that the connecting volcanic cone has been largely destroyed.

What was the main eruption like?

The eruption on 13th January was followed by a more significant, more explosive event at 5.15 pm local time on 15th January. The explosion generated enormous energy and created an umbrella cloud of ash, spreading the plume concentrically outwards instead of being dispersed in one direction by the wind. It was the most powerful eruption of the volcano since 1100 AD. The eruption was so loud it could be heard in New Zealand, some 2,383km (1,481 miles) from Tonga.

The initial height of the ash plume is an estimated 15.2km in altitude, later rising up to 30km high. The plume then spread to 260km in diameter before being distorted by wind. The graphic below provides a sense of the scale of the eruption.

The scale of the eruption of Hunga Tonga-Hunga Ha’apai volcano The scale of the eruption of Hunga Tonga-Hunga Ha’apai volcano

Why did the eruption occur?

Tonga’s volcanic islands are located on a destructive plate margin where the Pacific Plate meets the Australian Plate.

Tonga's Tectonic Setting

Tonga’s Tectonic Setting

The seismic tomography scan of the mantle below shows the Pacific Plate subducting below the Australian Plate. The water brought down by the slab is forced into the mantle above, producing the magma which forms the volcanic islands.

Seismic tomography scan of the Pacific Plate subducting the Australian Plate.

Seismic tomography scan of the Pacific Plate subducting the Australian Plate. Find out more about seismic tomography scans.

Why was the eruption so powerful?

The graphic below provides an overview of why the eruption could have been so powerful.

Why was the eruption of The Hunga Tonga-Hunga Ha’apai volcano so powerful

Why was the eruption of The Hunga Tonga-Hunga Ha’apai volcano so powerful? Source: Alistair Hamill, reproduced under a CC 3.0 licence with kind permission.

What were the effects of the eruption?

Following the eruption, people fled their homes and streets, and buildings flooded as tsunami waves crashed into Tonga’s main island of Tongatapu.

Twenty minutes after the eruption, a 1.2-metre tsunami wave is observed at Nuku’alofa, Tonga’s capital, according to the Australian Bureau of Meteorology. Waves reaching up to 15 metres (49 feet) hit the outer Ha’apia island group, destroying all the houses on the island of Mango, as well as the west coast of Tonga’s main island, Tongatapu, where 56 houses were destroyed or seriously damaged, the prime minister’s office said. People were evacuated from these islands.

Photos and videos emerged on social media of large waves flooding coastal areas, with reports of people making their way inland and to higher ground. Footage shows waves causing damage to buildings and infrastructure such as seawalls.

Experts believe the tsunami activity could have been triggered either by shock waves propagating through water or by a landslide on the undersea part of the volcano. The cause is currently unknown and may rely on sea bed monitoring to identify the cause.

A convoy of police and military troops evacuated King Tupou VI from his palace near the shore, and local news site Kaniva Tonga reported long lines of traffic as thousands of people attempted to reach higher ground across the main island.

By evening in the Pacific, the volcano is raining ash and tiny pebbles on neighbouring Tongan islands, with reports of darkness blanketing the sky.

Many residents slept in schools and churches.

Nuku’alofa was covered in a thick film of volcanic dust. As a result, there were concerns about contamination of food and water supplies and acid rain.

In addition to preventing aircraft from flying, ash hampers recovery efforts because it “buries gardens and impacts plants with consequences for food supply, and is likely to contaminate water supplies,” volcanologist Dr Chris Firth says.

The Pacific nation’s main undersea communication cable linking Tonga to Fiji was damaged. Unfortunately, it may be weeks before the cable can be repaired due to difficulty getting the repair ship from Papua New Guinea to Tonga and safety concerns for the ship’s crew, who would be operating in waters not far from the volcano. As a result, Tongans around the world may be forced to wait weeks for regular contact to resume.

An air pressure surge from the volcano’s eruption was recorded at seismic stations internationally, including in New ZealandAustralia, the US, and the UK, where two shockwaves are observed.

Aerial photographs were taken onboard a monitoring flight by the New Zealand defence force on Monday 17th January show some areas blanketed with ash, with damaged buildings, while others show parts of the country that appear unscathed.

In the hours following the eruption, tsunami warnings were issued across the Pacific, including in New Zealand, Australia, the west coast of the US, and Japan, where around 230,000 people across eight prefectures were ordered to evacuate.

According to the government, at least three people lost their lives in Tonga. In a statement, the government confirmed three deaths: two locals and a British national.

Two people drowned off a beach in the Lambayeque region of Peru after unusually high waves were recorded there. The country closes 22 ports as a precaution. The Californian city of Santa Cruz was hit by a tidal surge, damaging boats and flooding.

The eruption of a Tonga volcano sent ‘violent’ waves across the Pacific.


Six thousand barrels of oil were spilt into the ocean when the tsunami hit a boat loading oil at a refinery off the coast of Peru. The spill happened in an area rich in marine life such as seabirds, sea lions and otters.

Homes in the Tongan capital, Nuku’alofa, have their own water supply tanks, but most of them were filled with ash, so the water was not safe for drinking.

The United Nations said that about 84,000 people, more than 80% of the population, had been badly affected by the disaster. “They have been affected through loss of houses, loss of communication, what we understand is the issue with the water,” UN spokesperson Stephane Dujarric told reporters. “Water is really the biggest life-saving issue. Water sources have been polluted, water systems are down.”

Tongan man, Lisala Folau, climbed a tree on his home island before being washed away and eventually managing to reach the capital Nuku’alofa. Lisala was washed away by the tsunami and drifted and swam between islands for more than 24 hours.

What were the immediate responses to the eruption?

The Fijian government issued a tsunami warning, telling people in coastal parts to move to higher ground due to “larger than usual waves”. There were reports that some Fijian villages were inundated with water and families evacuated.

In Australia, Japan, Hawaii, Alaska and along the US Pacific coast, residents were asked to move away from the coastline to higher ground and pay attention to specific instructions from their local emergency management officials, said Dave Snider, tsunami warning coordinator for the National Tsunami Warning Center in Palmer, Alaska.

Australia’s Bureau of Meteorology issued an evacuation order for Lord Howe Island and warnings for a huge stretch of the mainland’s east coast. Sydney’s Bondi Beach was evacuated overnight, and a marine threat warning remained in place on Sunday morning Australian time.

The Australian defence force sent a surveillance plane on Monday 17th January 2022 to assess damage to critical infrastructure such as roads, ports and power lines.

There was little damage to the Fua’amotu International Airport’s south-eastern runway, but it was unserviceable following the eruption due to ash covering the runway. An operation to clear ash from the runway was underway, with vehicles and people visible from monitoring aircraft flown by New Zealand’s defence force. After the ash descended on Tonga, young men from villages surrounding the capital travelled to the airport to manually clear runways in order to make way for foreign aid planes

Australia and New Zealand pledged $1m in initial aid to Tonga. In addition, New Zealand dispatched two naval ships carrying water and other aid supplies.

The first aid flight arrived on Thursday 20th January. A New Zealand Defence Force plane landed following what Rear Admiral Jim Gilmour, commander of Joint Forces New Zealand, said was a “mammoth effort” to clear ash from the runway of Tonga’s international airport by hand. A strict no-contact protocol was adhered to as aid supplies were unloaded to reduce the risk of a Covid outbreak. Dubbed, contactless aid, emergency provisions are being sent in but personnel are not and strict Covid protocols are followed on delivery. Two years after the global pandemic began, Tonga is one of the few nations to remain Covid-free and has kept its borders shut to keep out the virus.

The HMNZS Wellington arrived on Thursday 20th January to survey the harbour to ensure its safety ahead of the arrival of the larger HMNZS​ Aotearoa on Friday, which is carrying supplies including 250,000 litres of water and a desalination plant.

Australia sent an air force plane that also arrived on Thursday 20th January loaded with essential supplies, including protective equipment and shelter materials. The government said it expected to send a naval vessel loaded with equipment, including helicopters, later on, Thursday or Friday.

On 20th January January 2022, a state of emergency was declared in the country until 13th February, the Tongan government announced.

Telephone links between Tonga and the rest of the world were also partially restored on Thursday 20th January, though restoring full internet connectivity is likely to take a month or more, according to the owner of the archipelago’s sole subsea communications cable. The country re-established some connections with the help of 2G internet and satellite telephone links.

Isolated communities on Tonga’s islands had to fend for themselves in the immediate aftermath of the eruption and tsunami.

What were the long-term responses to the eruption?

Coming soon

In the News

Tonga – Sky News

Tonga volcano and tsunami – BBC News

Tonga volcano – The Guardian

Going Deeper

The volcanic explosion in Tonga destroyed an island—and created many mysteries – National Geographic

Why the volcanic eruption in Tonga was so violent, and what to expect next – The Conversation

Tongan eruption sends atmospheric shockwaves around the world – The Royal Meteorological Society

The ‘perfect’ depth for a destructive eruption – BBC Inside Science Podcast

Tonga eruption: How its impact spread so widely and violently – BBC News

Retrieval Practice – Reducing Scaffolding

I’ve been thinking quite a lot recently about reducing scaffolding when using retrieval practice strategies. Multiple-choice questions are one of the most commonly used retrieval practice techniques; however, as discussed in the recent blog post, they have limitations – namely, they always include a correct answer. This is not to say they don’t have a use in retrieval practice. However, we should be aiming for students to complete short-answer questions for retrieval practice as they are required to produce the answer.

So, how can we achieve this? One possible approach might be to use multiple-choice questions in the first stage of retrieval practice. These could be used as starter activities or for homework. Once students demonstrate success using multiple-choice questions, the scaffolding could be reduced by providing students with short answer questions in the form of a crossword. Using a crossword, students can complete the questions in any order they like and, for those they find more challenging, the addition of letters from other words can prompt and support them in answering.

Removing Scaffolding

Removing Scaffolding

The final step is the introduction of short answer questions. If students continue to need support, the first letter of each answer could be provided. This can then be removed later.

To support geography teachers in reducing scaffolding for retrieval practice, a range of new resources are being developed for subscribers to Internet Geography Plus. We are creating a bank of resources in the form of multiple-choice questions, crosswords and short answer quizzes, each of which is available as an electronic document and interactive resource.

Internet Geography Plus subscribers already have access to a significant bank of multiple-choice questions in MS Word format and fully-customisable MS Forms and Google Forms Quizzes. In addition, we are currently working on crosswords and short answer quizzes.

Retrieval Practice: Multiple-choice or short answer questions?

Multiple Choice or Short Answer?

Saturday morning homework with the preteen – the part of the week when time normally standstill. A couple of weeks ago, biology homework involved her completing two quizzes. The first quiz was a multiple-choice quiz; the second was a short answer quiz. Both were based on content from the previous lesson. So, how did it go? My preteen flies through the multiple-choice quiz, getting all the questions correct on her first attempt. Next up, the short answer quiz. Despite covering similar content, she finds it a lot more challenging and finishes with a score of 63%.

After the homework was complete, we discussed the two approaches to quizzing. My preteen told me she preferred the multiple-choice questions because she found them easier to complete. Why? Because in many cases, she quickly identified the correct answer as seeing it triggered a memory response. When she did not immediately know the correct answer to a multiple-choice question, she worked through a process of elimination to find the correct answer. She also correctly guessed a couple of solutions. However, the short answer questions she found more challenging because she could not always recall the correct answer without a prompt being available. This is likely because she had not yet fully learned what had been taught in class. At this point, I will also add, that after looking at the multiple-choice questions, the distractors were not always plausible!

What surprised me was the difference in my daughter’s performance using multiple choice and short answer questions. Had my daughter not completed the short answer questions, both she and I might have come to the false conclusion that she knew her stuff about the topic being tested. Seeing my daughter using the two quiz formats for the first time led me to stop and reflect on how quizzing is used in learning.

A range of research suggests low-stakes testing/quizzing is beneficial to learners. There is no denying that frequent quizzing can reduce test anxiety; the work of Smith, Floerke, and Thomas in 2016 illustrates this. Students who receive an intervening test after the initial learning experience generally perform better on a later final test than subjects given only the final test. This phenomenon has come to be referred to as the testing effect. It has been demonstrated with diverse study stimuli, including word lists (Darley & Murdock, 1971), paired associates (Runquist, 1986), pictures (Wheeler & Roediger, 1992), general knowledge facts (McDaniel & Fisher, 1991), and prose passages (LaPorte & Voss, 1975; for a review, see Roediger & Karpicke, 2006a).

However, how often do we reflect on the format low-stakes quiz/test questions should take? Multiple choice and short answer formats are probably two of the most common. When completing short answer questions, students must think of and produce the correct answer. In contrast, multiple-choice questions provide several possible solutions and require the learner to choose the correct one. But which is best? 

Research by Kang, McDermot and Roediger (2007)1 suggests that short-answer questions improve learning more than multiple-choice questions as they require students to produce the answer. So, does this mean we need to stop using multiple-choice quizzes in favour of short answer quizzes? Certainly not. In geography, students are often faced with multiple-choice quizzes in the exam, so they need to be well versed in completing them. Additionally, a study by Smith and Karpicke (2014)2 has indicated that students who practised retrieval (either multiple choice or short answer quizzes) performed better than those in a control group. However, the differences between the performance of the students using the two forms of retrieval (short answer and multiple-choice) were small.

Considering this, it is clear that both approaches to quizzing for retrieval practice have a place in geography. However, it is worth considering when each is most appropriate. For example, in the short term, after teaching a concept or topic, multiple-choice questioning (containing effective distractors – take a look at these tips) might be well suited to support embedding learning. Following this, the scaffolding that multiple-choice questions can provide to students can be removed, transitioning to short answer questions to check for knowledge and understanding. This way, students have to work harder to by having to retrieve their answers from memory.

Tectonics Short Answer Questions

Tectonics Short Answer Questions available to Internet Geography Plus subscribers

To support Internet Geography Plus subscribers in developing the use of short-answer questions. We’re creating a bank of questions and answers that can be shared with students in Word documents along with a bank of self-marking Google Forms/Microsoft Forms that subscribers can copy over to their accounts. To get the ball rolling we’ve added a bank of short answer questions (and answers) covering hazards, tectonics and plate margins in Word, Google Form and Microsoft Form format that Internet Geography Plus subscribers can access now. Log in or take out a low-cost subscription to Internet Geography.

We’ve also developed an example of a hybrid quiz containing multiple choice and short answer quiz questions available in the 4Rs of Revision area in Internet Geography Plus.

If you’ve experience combining the use of multiple-choice and short answer questions as part of your retrieval strategy, please share in the comments below.


  1. Kang, McDermot, and Roeriger (2007), Test format and corrective feedback modify the effect of testing on long-term retention – https://www.scinapse.io/papers/1981846272#fullText.
  2. Smith and Karpicke (2014), Retrieval practice with short-answer, multiple-choice, and hybrid formats

Geography in the News Self-Marking Homework Pilot

Geography in the News Self-Marking Forms

From this week until the half-term holiday in October we are piloting a new approach to Geography in the News homework. Each week will we be sharing a quiz in Google Forms and Microsoft Forms based on a news article relevant to the geography curriculum. Teachers can copy the form with the click of a link then share it with students to complete for homework. Each form will be self-marking to help reduce workload. This week we explore the gas shortage facing the UK this winter covered in an article on the BBC news website.

We’ve also recently released Geography in the News Plus for subscribers to Internet Geography Plus. Each week we publish GCSE exam-style questions based on an event in the news. These can be downloaded from the member area of Internet Geography Plus, just log in to access.

Geography in the News is free for teachers to access. It is funded by the lovely people who subscribe to Internet Geography Plus. If you don’t already subscribe please consider supporting us by taking out a low-cost annual subscription starting from just £24.99. To access the free Geography in the News forms please head over to the Geography in the News area of Internet Geography.

If your are copying the Google Quiz please make sure you are logged into your Google account first.

Tweet Treats #13

It’s been a while since we shared Tweet Treats, a collection of useful tweets relating to #geography and #geographyteachers. The world of Twitter can be a busy place so we’ve pulled together some great tweets recently posted on Twitter.

The collection of tweets below are in no particular order.

Looking for ready-made displays? Take a look at the resources shared by Kelly Pippin.

Loving this great activity to challenge locational knowledge by Chris Hoare.

Teaching volcanoes at convergent plate boundaries and an editable diagram to download from Luke Taylor.

An incredible set of threads containing subject knowledge updates by Anti-racist Geography Curriculum. This is a must-read!

Check out the recent RGS-IBG podcast with Ofsted inspector and subject lead Iain Freeland!

Kate Otto shares some great scenario questions being used to encourage thinking.

Alistair Hamill shares a video on how he uses GIS to teach biomes.

BBC Weather has shared a great video exploring whether global warming will make devastating storms like Hurricane Ida more likely?

Equipment for Microclimate Investigation

Coastal erosion at Skipsea

Skipsea is a village located 6 miles north of Hornsea and 10 miles south of Bridlington on the Holderness Coast, East Yorkshire. Skipsea lies on soft boulder clay and experiences the highest rate of erosion in Europe. A combination of stormy weather and rising sea levels caused more than 10 metres of the cliff to disappear from a 2-mile stretch of coast in just nine months last year, compared with the annual average of 4 metres. In just six months, three strips of coastline lost nearly double what they expected to lose in a year.

The average annual erosion rate remains about 2 metres a year for the 52-mile Holderness coastline. In Skipsea, there is anger that sea defences have protected neighbouring towns and villages such as Hornsea and Bridlington but their parish, with its population of about 700, has not. Sea defences are decided on a cost-benefit analysis, with large urban areas and important industries prioritised over farmland and individual houses. On that basis, Skipsea must brave the waves.

Until recently, 19 properties sat adjacent to the coast along Green Lane. Now, there are 16. It has been suggested that the remaining residents will need to vacate their properties within a couple of years. However, a single erosion event could put the properties at imminent risk within the next year.

Green Lane properties at Skipsea

Green Lane properties at Skipsea

Some residents on Green Lane feel the council has not done enough to protect them from erosion or help them to move nearby. As it stands, they have to pay around £6000 towards the cost of demolishing their homes. The East Riding of Yorkshire council provides some financial support to help residents cover the cost of demolishing their properties – which can cost between £15,000 and £40,000 – but they are continuing to ask the Government for funding.

Vacant plots on Green Lane

Vacant plots on Green Lane

La Soufrière Eruption 2021

JCQ GCSE Geography Grade Descriptors

The JCQ have published guidance for determining GCSE/A Level grades for 2021.

How much use the grade descriptors are is another question.

Below are links to published resources.

Quick links: 

Guidance statement – web page

Guidance Document – PDF file

All guidance downloads – web page with links to PDFs

GCSE Grade Descriptors (all GCSEs) – PDF

GCSE Geography grade descriptors in Word format – provided by Internet Geography

Internet Geography has developed assessment materials for AQA GCSE geography, in the style of past papers and come with a comprehensive mark scheme. There are available to Internet Geography Plus subscribers. Log in here or access for one year with a low-cost subscription.