Geology for Global Development

Heather Britton

Heather Britton: Sinkhole Occurrence and Mitigation

Sinkholes are often overlooked geohazards which, although far less destructive in the short-term than earthquakes and landslides, can be catastrophic to life and severely impact the built environment. This post will explore how these features form and the strategies that have been adopted to predict their appearance. It will also consider how urbanisation in karstic areas is accelerating sinkhole formation and what can be done to mitigate these effects.

Sinkholes form most commonly in karstic terrain – topography shaped by the dissolution of soluble rocks such as limestone, gypsum and dolomite. This dissolution creates cavities beneath the ground surface, and the subsidence of the land into these cavities creates sinkholes. Karstic regions are generally associated with three varieties of sinkhole, displayed in the figures below.

  • Figure 1 – Rainfall and surface water percolate through joints in the limestone. Dissolved carbonate rock is carried away from the surface and a small depression gradually forms. On exposed carbonate surfaces, a depression may focus surface drainage, accelerating the dissolution process. Debris carried into the developing sinkhole may plug the outflow, ponding water and creating wetlands. (Source: USGS Water Science School)

    The first are dissolution sinkholes, which form when dissolution is concentrated in a particular area, often along pre-existing joints or fractures within the rock where groundwater flow preferentially occurs. This causes the land to sink in this area and the result is a sinkhole.

  • Cover-subsidence sinkholes are characterised by a thick overburden of granular sediment which gradually falls into an underlying cavity.
  • The final variety, cover-collapse sinkholes, are undoubtedly the most dangerous as they can develop over a period of hours. Cover-collapse sinkholes occur where cohesive material overlies a soluble bedrock. When dissolution occurs in the carbonate/evaporite the overlying cohesive substance will form an arch over the cavity, making it very vulnerable to collapse. In 2013 Jeff Bush disappeared into one such sinkhole as he slept in his home in Seffner, Florida, demonstrating just how catastrophic these geohazards can be.


Figure 2 – Cover-subsidence sinkholes, where a thick, overlying, sandy sediment layer fills an underlying cavity, usually produced through carbonate/evaporite dissolution. Source: USGS Water Science School

Figure 3 – Cover-collapse sinkhole formation. Due to the cohesive nature of clay and similar sediment, these sinkholes often do not form gradually and instead tend to appear very suddenly, creating the greatest risk to human life and property. This is usually as a result of an influx of water, causing the layers in the clay to slide over one another. Source: USGS Water Science School

Worryingly, the appearance of sinkholes seems to be on the increase. Urbanisation is accelerating the rate at which sinkholes form, as it is intrinsically linked with processes such as construction and mining. Groundwater pumping associated with construction work changes the natural drainage patterns of the land, leading to dissolution in regions where it has not been seen before. On top of this, increased agriculture to feed the growing population involves the drainage of organic soils, leading to the runoff of organic carbon and the production of highly acidic water sources (pH 3.4-4 recorded in some instances) which inevitably accelerates the dissolution of soluble bedrock. Groundwater pumping in particular was responsible for 80% of identified subsidences in the US where sinkholes are a problem across many states. And the issue is not limited to the US – karstic regions around the world are seeing an increase in the number of human induced sinkholes, for example those which effecting the Madrid-Barcelona High Speed railway. Human activities are undoubtedly impacting sinkhole formation, be it through mining, agriculture or construction.

Aerial view of a large collapse structure, the Tres Pueblos sink, along the Rio Camuy, which exits on the far side of the sinkhole. Solution of underlying rock removed the support and the roof of soil and thin bedrock collapsed into the void. This produces what is known as karst topography. (Courtesy United States Geological Survey)

So what is the best way of allowing development to occur without exacerbating the anthropogenic effect that urbanisation can have on sinkhole formation? One of the simplest and most frequently implemented solutions is to avoid building in regions that may develop sinkholes, or have been shown to be prone to sinkholes in the past. This planned development can be implemented on a small scale, but it is unrealistic to avoid the development of large karstic regions altogether. Carefully considering the drainage networks of new builds and infrastructural projects may help to minimise the effects of development on sinkhole evolution – but sometimes the development pressure is much greater than any impetus to properly consider the state of the land which is being built on.

Currently our best solution to urbanisation in karstic areas is to monitor sinkhole development and attempt to detect them as soon as they appear. Monitoring is possible through geomorphological mapping and the use of GIS and DEM (Digital Elevation Mapping), whilst detection can be achieved with relative ease using geophysical methods (e.g., seismic data and radar). Although not preventative, such techniques do allow sinkholes to be identified early in their development, therefore they can be either avoided or filled before any serious damage is attained.

Even knowing where developing sinkholes lie does not stop construction occurring over them. A short term solution to a developing sinkhole is to fill it, often with concrete, as was done in Zaragoza, Spain. Here the sunken region was waterproofed before being injected with concrete. Whilst it might be thought the initial waterproofing step would end the cycle of dissolution and sinkhole formation, this action was actually seen to increase karstic activity. Filling sinkholes with concrete is not a sustainable solution – it does not prevent sinkholes from continuing to subside (although it may prevent catastrophic collapse) and too much concrete would be required to fill all sinkholes which pose a threat to human property. Other materials are in greater abundance, however, for example rubbish. It is highly unlikely that we will grow short of this ‘resource’ and the planet is currently in need of more landfill sites. The primary risk of this technique is the contamination of groundwater and other water sources – even if rubbish was only used in regions where there was a low risk of water contamination, the danger that groundwater flow would change and begin to poison sources of drinking water would always exist, making this a risky strategy, particularly in regions undergoing heavy urban development or in tectonically active areas. Geologists are working towards solutions – This student paper looks into how sinkholes can be stabilised, removing the danger of collapse – but many sinkholes have unique features which set them apart from the rest, therefore one solution may not be appropriate in all instances.

As the number of sinkholes grows, it is becoming more and more important that we develop better ways of dealing with and preventing this geohazard. Currently our efforts are limited to planning around sinkholes and detecting and monitoring their evolution early, but with urbanisation spreading into karstic regions around the world further work must be done to reduce the risk that this hazard holds for communities. Research is ongoing, and hopefully in the near future will yield not only better detection and mitigation technologies, but more effective and sustainable methods of dealing with sinkholes once they form.

Heather Britton: India’s Energy-Climate Dilemma

Heather Britton is one of our new writers, today reporting on a summary of this paper by Andrew J Apostoli and William A Gough, covering the difficulties of pursuing reduced greenhouse gas emissions whilst fuelling one of the largest populations on the planet – India. The actions of this country are contributing to the eventual achievement of UN Sustainable Development Goals 7 and 13 – Affordable and Clean Energy, and Climate Action respectively.

India makes up 18% of the world’s population (1.2 billion people) with this value predicted to rise to 1.5 billion by 2030. Like many countries in the Global South, India is currently reliant upon fossil fuels to meet its energy demands, but it lacks the natural resources to provide energy for its people in this way – already 80% of its oil is imported, and this is likely to increase in the coming years. On top of this, India’s current energy production is falling short of their present requirements, with only 44% of households having access to electricity and 600,000 villages yet to be connected to the national electricity network.

You could be forgiven for thinking, therefore, that reducing carbon emissions would not be a priority, with the more pressing issue of making sure all Indians have access to energy taking precedence. This, however, is far from the reality, and although per-capita emissions are predicted to increase significantly as a result of the demands of a growing population, India’s renewable energy sector is ranked fifth in the world (Figure 1), and plans are in place to ensure that this sector’s growth does not stop here.

Figure 1: Global renewable energy investments. Source: Bloomberg New Energy Finance, Global Trends in Renewable Energy Investment, 2016

Although a factor in this statistic is the huge (and expanding) population of the country, it seems that India truly are passionate about pursuing a sustainable future. A survey recently revealed that many Indian citizens were happy to pay a carbon tax due to their awareness of the environment and the problems it is currently facing. To some, the environmental conscience of the country is seen as exacerbating India’s energy problem – if India can’t generate enough energy to ensure that all of its people have access to a sizeable and dependable energy source, why restrict the use of some of the most reliable methods of energy generation on the planet? – Others however have seen it as an admirable step in pursuit of sustainable development.

India has adopted ambitious targets to reduce greenhouse gas emissions through climate change policies and financial incentives to promote the development of new renewable energy initiatives, but it is currently unclear whether this will be enough for India to overcome its present day energy difficulties and meet the environmental promises that they have made both to their public and the global community (e.g. pledging to reduce emissions by 20-25% by 2020, although this is not legally binding).

Figure 2: Smog in New Delhi, India. Source: Prakhar Misra (distributed via

The landscape and climate of India are well suited to many forms of renewable energy generation, making these options financially viable. It is clear that if India is to achieve its goal of supplying affordable energy to allow economic growth in an environmentally-conscious manner, renewable energy must be heavily invested in, enabling technological developments to be made in this industry.

The Indian government has produced a number of funding initiatives to encourage such investment: for example the ‘National Action Plan on Climate Change’ (NAPCC) was formed ‘to make India a prosperous and efficient economy that is self-sustaining for both present and future generations while confronting climate change’ (Apostoli and Gough, 2016). Its aims include reducing poverty, reducing the anthropogenic effects of climate change and developing technologies at a fast pace to ensure the regulation and mitigation of greenhouse gases.

Other funding initiatives include the coal tax, which has risen form 50 rupees per tonne of coal in 2010 to 400 rupees per tonne in 2016, the money from which is used to finance the national clean environment fund. Up to 2015 this fund had developed 46 clean energy initiatives, and has allowed further projects to take off since. In addition, tax-free bonds were offered from 2015-2016 for the financing of renewable energy initiatives, valued at around $800 million.

India therefore has succeeded in creating motivation for the development of renewable energy and has a plethora of methods of renewable energy generation available – the details for some of which I have outlined below:

Hydropower: With altitudes ranging from the highs of the Himalayas to lows of the Ganges delta, India’s landscape is perfectly suited to both large and small scale hydropower plants. As of 2013 17%  of the total electricity generated in India was from hydropower stations, second only to coal, demonstrating the potential for the development of this field in the future.

Solar: Sitting between the tropic of cancer and the equator, India is ideally situated for the generation of energy through the use of solar cells. Solar energy has the potential to surpass India’s annual energy consumption and allow it to become a global leader in solar energy, although the initial costs of the solar cells required is considerable. With schemes such as the ‘National Solar Mission’, aiming to have 22 GW of solar capacity by 2022, the solar sector in India is expected to expand rapidly.

Wind: There is huge potential for the wind industry. Wind generation is not only the largest growing renewable energy sector in India, but is also experiencing a recent rise in social acceptability, leading to the prediction that in 2020 wind energy will save 48 million tonnes of CO2.

Biomass: This is an incredibly important energy source for India, as 70% of the country’s population rely on it for energy. Currently, however, biomass is being used inefficiently, exposing children and women to high levels of indoor pollution. Policies have been developed to encourage more efficient and cleaner utilisation of this abundant fuel, but there is still a long way to go in improving the use of biomass.

Figure 3: Landscape of the Indian Himalaya, well suited to many methods of renewable energy generation. Source: Yuval Sadeh (distributed via

The progress in the renewable energy industry sounds promising, but as ever problems are arising. Last year the Indian state Tamil Nadu generated more energy using solar cells than it required – but this energy could not be passed on to other states as the grid was not sophisticated enough to  connect this excess of renewable energy to neighbouring states. It is clear that developing methods of renewable energy generation is of great importance, but without careful planning much of the future renewable energy generated may go to waste.

In conclusion, sustainable development is of pressing concern to India, a country which houses a significant proportion of the world’s poor. There is currently heavy demand for fossil fuels, as the country undergoes unprecedented economic growth, rapid population increase and industrialisation. This places pressure not only on the national grid, but on unsustainable resources which will be exhausted under current consumption rates.

In response to these challenges India has invested heavily in the deployment of renewable energy strategies. With a combination of financial incentives, taxes and subsidies, India has caused a surge in renewable energy schemes, working to exploit the country’s landscape. Although it is still in the early stages of development, India’s dedication towards renewable energy will result in greater energy security for the world’s second largest population, providing them with the independence to facilitate economic growth whilst reducing their greenhouse gas emissions. There is certainly more work to be done, but the impetus that India has demonstrated in finding solutions to their energy crisis will hopefully result in a happy ending for this sustainable development story.

Read more: Andrew J Apostoli and William A Gough, (2016) India’s Energy-Climate Dilemma: The Pursuit for Renewable Energy Guided by Existing Climate Change Policies, Journal of Earth Science & Climatic Change, 7:362.

**This article expresses the personal opinions of the author (Heather Britton). These opinions may not reflect an official policy position of Geology for Global Development. **

Introducing Our New Authors (2) – Heather Britton

Exploring Zhangjiajie National Park, Hunan province, China

We’ve been introducing you to a couple of new faces on the GfGD blog, bringing fresh ideas and perspectives on topics relating to geoscience and sustainable development. We’re delighted to have their input, and look forward to their posts. Today we interview Heather Britton – a recent graduate of the University of Cambridge (UK). 

Tell us a bit about yourself.

I’ve recently graduated with a Master’s in Earth Sciences and have just returned from a summer of travelling around China. Like many graduating geoscientists, I’d like to do work that has a positive impact on the world and GfGD has helped to show me how I might be able to do that. I am looking forward to getting more involved with the charity through these blog posts and hope not only to enlighten others, but to learn myself about the interface between geoscience and international development.

I love spending time outdoors – I enjoy hiking and play rugby regularly. I also travel as much as I can; I have been accused by family of only studying Earth Sciences for the travel opportunities it brings, but in truth this is just one of the many perks of studying this versatile subject.

How did you become involved with GfGD?

I attended the Geology for Global Development annual conference last year, and was really inspired by the talks, poster session and discussions held there. If anyone is hesitant as to whether or they not they should attend, I highly recommend it [editor: details of 2017 event can be found here!]. The conference demonstrated to me that it was not only possible to have an ethical career using my degree in Earth Sciences but that it is crucial for the geosciences to be considered when undertaking development projects. From there I took a greater interest in international development and the involvement that the geosciences could have. I wanted to get more involved in the work of GfGD, so when I saw their call for volunteers I was quick to sign up and here I am.

What did you do in your Master’s?

In my final year I specialised in climate science, palaeontology and some petrology, although I find the whole spectrum of Earth Sciences interesting and you can expect my posts to cover a wide range of geoscience fields.

My research project was palaeontology based and I confess not particularly development related! The aim of the project was to calculate the lifespan of ammonites from the growth lines on their aptychi (calcitic plates thought to either be the lower jaw structure or opercula of certain species of ammonite). On top of this I looked into the palaeobiology and palaeoecology of ammonites, using oxygen isotopes to estimate the temperature of the water in which these organisms once lived. I enjoyed the research and am considering doing a PhD in the future.

What can we expect your blogs to cover?

I hope to cover a wide range of topics so that I can appeal to the interests of as many people as possible. I am also looking forward to summarising papers covering the geosciences and international development and connecting these with the UN Sustainable Development goals which underpin so much of the work that GfGD does.

An example of an issue I have been reading about recently is sustainable coral reef management and how developing communities can benefit from the sustainable use of the resources that these environments have to offer, for example through tourism. Regional co-operations are popping up in highly affected areas working to protect reef environments but there is still a lot of work to be done to preserve these unique and hugely biodiverse environments and make local people aware of what does and does not damage these sensitive ecosystems. I also have an interest in how best to make vulnerable communities more resilient to disasters, be they earthquakes, tsunamis or hurricanes like those that have been in the headlines these past few weeks.

Plans for the future?

My dream job would be using my knowledge of geoscience in an ethical way to make a positive difference to the world, whilst involving a lot of travel. For now, however, I am more than happy to invest time in writing blogs for this fantastic charity – it is certainly a step in the right direction.

**This article expresses the personal opinions of the author (Heather Britton). These opinions may not reflect an official policy position of Geology for Global Development. **