Natural Hazards

Imaggeo on Mondays: Ice forming on Chesapeake Bay

Imaggeo on Mondays: Ice forming on Chesapeake Bay

Sandwiched between the U.S states of Mayland, Delaware, Pennsylvania, New York State, the District of Columbia and Virginia, lies Chesapeake Bay, the largest estuary in North America. It is of huge ecological importance: “the bay, its rivers, wetlands and forests provide homes, food and protection for countless animals and plants”, says the Chesapeake Bay Program. Up to 150 major rivers and streams feed into the bay’s watershed.

Geologically speaking, Chesapeake Bay isn’t very old. As recently as 18,000 years ago the bay was covered by dry land. Global sea levels were up to 200m lower than they are at present and the last of the great ice sheets to cover America was at its peak. The rivers which flowed along the east of the continent had to cut valleys in what is now the bay bottom, to reach the continental shelf, and drain out to sea.

Fast forward 8,000 years and rising global temperatures caused the ice sheets to melt rapidly. Global sea levels started to rise, flooding the continental shelf and coastal areas, which now make up the modern-day estuary.

The process was helped along by a remarkable, much older geological feature. During the late Eocene, 35 million years ago, the Atlantic margin of the U.S was struck by a 3.5 km bolide (an asteroid or meteorite). The impact crater is located about 200 km south of Washington D.C., buried below 300 -500 m of sediments in Chesapeake Bay. Though the crater didn’t form the estuary, it did create a long-lasting depression in the area which helped determine the location of the bay.

Landsat satellite picture of Chesapeake Bay (centre) and Delaware Bay (upper right) – and Atlantic coast of the central-eastern United States. Credit: Landsat/NASA. Distributed by Wikimedia Commons.

Further reading

The Chesapeake Bay Bolide Impact: A New View of Coastal Plain Evolution: USGS Fact Sheet 049-98.

Chesapeake Bay Program

Landsat Images Offer Clearer Picture of Changes in Chesapeake Watershed (Nasa Landsat Science)

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at

Malawi High School Teacher’s Workshop on Natural Hazards

Malawi High School Teacher’s Workshop on Natural Hazards

In July 2017, Professor Bruce Malamud and Dr Faith Taylor from King’s College London travelled to Mzuzu, Malawi to work in collaboration with Mr James Kushe from Mzuzu University, Malawi. They delivered an EGU funded workshop at Mzuzu University to high school teachers on natural hazards, with major funding provided by EGU, and also supported by Urban ARK and Mzuzu University. Faith and Bruce explain more about the trip…

Malawi is a small (118,000 km2) landlocked country in south eastern Africa, often referred to as the ‘warm heart of Africa’ due to its stability, safety, beauty and warm welcome to visitors. Yet behind this warm welcome, life for many in Malawi is hard; with an average GDP per capita of US$0.82 per day, high (although improving) prevalence of HIV-AIDs, tuberculosis and malaria and a range of natural disasters including earthquakes, floods, lightening, hail, strong winds and drought.

Although we are biased, we think life is particularly hard for Malawian Geography teachers who have a great responsibility to shape the next generation of big-thinkers and problem-solvers against the challenges such as (i) large class sizes, (ii) limited opportunity for teachers’ continued professional development and (iii) under-resourcing of schools.

With this in mind, Bruce, James and I applied for EGU funding to run a workshop for teachers on natural hazards, focusing particularly on: (i) collating and developing low-cost teaching demonstrations, (ii) equipping teachers with further information about natural hazards and (iii) learning more about their home city of Mzuzu as a resource for field trips.

Professor Bruce Malamud demonstrating seismic waves using a giant slinky.

In the months running up to the workshop, we prepared 16 Gb USB sticks for each teacher which included >35 teaching demos that we had created and/or reviewed, and then trialled, 77 videos that we selected from the many out there, 11 digital posters and 16 factsheets and 14 Powerpoint lectures from our own teaching. We also started to order a few resources that would be hard to come by in Malawi, such as slinkies for teaching about earthquake waves and mento tubes for demonstrating volcanic eruptions (try explaining a suitcase of slinkies to a customs official!).

In Mzuzu, James visited each highschool to explain the purposes of our workshop and get local interest, planned a fieldtrip to the Massassa region and started to purchase locally available resources for teaching demonstrations, such as jars and sand for teaching about the angle of repose with regard to landslides.

Upon arrival at the Mzuzu University library, where we held the workshop, we were greeted by 27 high school teachers who had travelled from up to a couple of hours away to spend three days with us. The schools they came from varied in terms of resourcing, teachers’ background and experience, but all teachers were enthusiastic about the opportunity to learn more (note to others, teachers were particularly keen on further EGU funded workshops on other topics!).

Over the three days, we delivered interactive undergraduate level lectures on a range of natural hazards, so that teachers would better understand the process behind many of the hazards, interspersed with over two dozen activities and teaching demonstrations that they could bring back to the classroom. We also had a half day microadventure facilitated by one of the teachers to a local area that had been affected by flooding and landslides. This was a good reminder that geography starts on the doorstep, and does not require expensive fieldtrips to exotic destinations to help students experience environmental phenomena and solidify their classroom based learning. There were also opportunities for the teachers to share some of their best practice – and from this, we hope the seed has been sown for teachers to establish their own professional network for sharing ideas and resources.

We have travelled to Malawi multiple times over the past few years as part of our work on the Urban ARK project where we look at multi-hazard risk to infrastructure. From this work, we know how challenging it can be for information and ideas to flow to those experiencing and managing risks. We left Malawi feeling hopeful that through those 27 bright and enthusiastic teachers, we might reach >2000 students, and through those students we might also reach their friends and family to help reduce disaster risk across the Mzuzu region.

In the coming months we will share some of the resources we generated and collated online. There is a clear need for further workshops like this across Malawi, and an appetite for building a network of teachers. It took a lot of planning and partnerships with local academics but we would strongly encourage others to consider running similar workshops for teachers in the warm heart of Africa.

By Faith Taylor and Bruce Malamud, King’s College London

September GeoRoundUp: the best of the Earth sciences from around the web

September GeoRoundUp: the best of the Earth sciences from around the web

Drawing inspiration from popular stories on our social media channels, as well as unique and quirky research news, this monthly column aims to bring you the best of the Earth and planetary sciences from around the web.

Major story and what you might have missed

This month has been an onslaught of  Earth and space science news; the majority focusing on natural hazards. Hurricanes, earthquakes and volcanic eruptions have been dominating headlines, but here we also highlight some other natural disasters which have attracted far fewer reports. Quickly recap on an action-packed month with our overview, complete with links:


Thought the Atlantic hurricane season is far from over, 2017 has already shattered records: since 1st June 13 storms have been named, of which seven have gone onto become hurricanes and two registered as a category 5 storm on the Saffir-Simpson Hurricane Wind Scale. In September, Hurricanes Irma, Katia and Jose batter Caribbean islands, Mexico and the Southern U.S.; hot on the heels of the hugely destructive Hurricane Harvey which made landfall in Texas and Louisiana at the end of August. Images captured by NASA’s Operational Land Imager (OLI) on the Landsat 8 satellite show the scale of the damage caused by Hurricane Irma; while photos reveal the dire situation unfolding in Puerto Rico after Hurricane Maria.  OCHA, the United Nations Office for the coordinate of Human Affairs, released an infographic showing the impact the 2017 hurricane season has had on Caribbean islands (correct of 22nd September).


At the same time, two powerful earthquakes shook Mexico in the space of 12 days causing chaos, building collapse and hundreds of fatalities.

Rumbling volcanoes

In the meantime, all eyes on the Indonesian island of Bali have been on Mount Agung which has already forced the evacuation of almost 100,000 people as the volcano threatens to erupt for the first time in 54 years. Unprecedented seismic activity around the volcano has been increasing, though no eruptive activity has been recorded yet.

Further south, the government of Vanuatu, a South Pacific Ocean nation, declared a state of emergency and ordered the evacuation of all 11,000 residents of Ambae island, as activity of its volcano, Manaro, increased. The New Zealand Defence Force (NZDF) sent an aircraft to fly over the volcano on Tuesday and discovered plumes of smoke, ash and volcanic rocks erupting from the crater.

Map of volcanic hazards for Ambae in Vanuatu. Credit: Vanatu Meteorology & Geo-hazard Department (vmgd).

The rainy season floods

The summer months mark the onset of the rainy season in regions of Sub-Saharan Africa which experience a savanna climate. Across the Arabian Sea, including the Indian subcontinent and Southeast Asia, also sees the onset of the monsoon.

Since June, widespread flooding brought on by heavy rainfall has left 56 dead and more than 185,000 homeless in Niger, one of the world’s poorest countries. But the crisis is not restricted to Niger, throughout the summer floods (and associated land and mudslides) in Africa are thought to have claimed 25 times more lives than Hurricane Harvey did.

Meanwhile Mumbai struggled when the heaviest rainfall since 2005 was recorded on 29th August, with most of Northern India experiencing widespread flooding. So far, the UN estimates that 1,200 people have lost their lives across Nepal, India and Bangladesh as a result of the rains. The Red Cross estimates that at least 41 million people have been affected by the flooding and causing the onset of a humanitarian crisis.

Record breaking temperatures and fires

Australia’s record-breaking spring heat (Birdsville, in Queensland’s outback, broke a weather record as temperatures hit 42.5C and Sydney recorded its hottest ever September day) combined with an unusually dry winter means the country is bracing itself for a particularly destructive bushfire season. Already fires rage, uncontrolled (at the time of writing), in New South Wales.

The western United States and Canada suffered one of its worst wildfire seasons to date. Earlier this month, NASA released a satellite image which showed much of the region covered in smoke. High-altitude aerosols from those fires were swept up by prevailing winds and carried across the east of the continent. By 7th September the particles were detected over Ireland, the U.K and northern France, including Paris.

Europe’s forest fire has been hugely devastating too. Much of the Mediterranean and the region North of the Black Sea continues to be in high danger of forest fires following a dry and hot summer. Fires are active in the Iberian Peninsula, Greece, and Germany (among others). Over 2,000 hectares were recently scorched by wildfires in the central mountainous area of Tejeda in Gran Canaria.

Links we liked

  • This month saw the end of NASA’s Cassini spacecraft and ESA’s Huygens probe’s spectacular journey to Saturn. After two decades of science, the mission ended on 15th September as the spacecraft crashed into the giant planet.
  • The last day of August marks the end of the Greenland snow melt season, so September was busy for scientists evaluating how the Greenland ice sheet fared in 2017.
  • “Few disciplines in today’s world play such a significant role in how society operates and what we can do to protect our future,” writes Erik Klemetti (Assoc. Prof. at Denison University), in his post on why college students should study geology.
  • The BBC launched The Prequel to its much anticipated Blue Planet II, a natural history progamme about the Earth’s oceans. Narrated by Sir Sir David Attenborough, the series will featured music by Hans Zimmer and Radiohead. The trailer is a true feast for the eyes. Don’t miss it!

The EGU story

Is it an earthquake, a nuclear test or a hurricane? How seismometers help us understand the world we live in.

Although traditionally used to study earthquakes, like the M 8.1 earthquake in Mexico,  seismometers have now become so sophisticated they are able to detect the slightest ground movements; whether they come from deep within the bowels of the planet or are triggered by events at the surface. But how, exactly, do earthquake scientists decipher the signals picked up by seismometers across the world? And more importantly, how do they know whether they are caused by an earthquake, nuclear test or a hurricane?

To find out we asked Neil Wilkins (a PhD student at the University of Bristol) and Stephen Hicks (a seismologist at the University of Southampton) to share some insights with our readers earlier on this month.

Record-setting forest fires in 2017 – what is to blame?

Record-setting forest fires in 2017 – what is to blame?

Forest fires have once again seized the public consciousness in both Europe and North America. Extreme drought and temperatures contributed to a tinderbox in many forests, and have led to deadly fires across Europe and record-breaking, highly disruptive fires in the USA and Canada, from where I’m currently writing.

A simple way to understand fire is by thinking about the fire triangle – the three pieces that need to combine to produce fire: heat, oxygen, and fuel. While the concept of the fire triangle offers simple insights into the cause of a fire, each of the three factors are subject to a number of controls.

The availability of fuel in particular is affected by a whole range of influences, from tree species variations, to the impact of pests, to the prior history of wildfires. In many cases there will be a multitude of reasons for both the rate that a given fire spreads, and the spatial extent to which it burns. The extensive media coverage of this year’s record-breaking fire season provides a useful opportunity to explore some of these factors, and how they might have contributed to the fires that we’re seeing this year.

Multi-tiered fires

Not all forest fires are equal. The forestry service in British Columbia defines 6 different levels of fire, ranging from slow burning of peat below the surface of a forest (a ground fire), through the burning of scrub and ground level debris (surface fire), to far harder to control conflagrations that consume the canopy of the trees (a crown fire).

Each type of fire consumes fuel from different levels of the forest, and a transition from a lower to higher level requires at a minimum that there is enough flammable material in the upper layers of the forest. As such, the history of fire in a given stand of woodland will have a significant effect on the potential for future fires; a prior surface fire could remove the under-brush and limit the future fire risk.

Many older trees in a forest can have fire scars from previous, smaller fires that have not burnt them entirely, demonstrating that not all fires make the transition to crown fires. In the US, the largest 2-3% of wildfires contribute 95% of the total area burned annually, and these are generally the largest crown fires. For these large fires, the conditions must be optimal to reach the canopy, but once they make this transition they can be very difficult to stop.

Although the largest fires require a specific set of conditions, the transition to large fire can lag for a long time behind the initial trigger of a fire:

“Once ignited, decaying logs are capable of smouldering for weeks, or even months, waiting the time when prevailing conditions (hot, windy, and dry) are conducive for expansion into a full-blown forest fire,” write Logan & Powell in 2001.

The initial trigger in natural settings for the fire is generally lightning, or in rare cases the intense heat from lava flows. However, a recent study has shown that in the continental US, 84% of fires are started by humans. This can range from discarded cigarettes to prescribed fires that have raged out of control.

So, we now have a simplified understanding of the requirements for a fire, but perhaps the more important question remains: why do they spread?

What fans the flames?

So what are the processes that control the strength and spread of a fire? Certain aspects, like climatic conditions, tend to set a long-term propensity for wildfire, while other short term effects define the local, immediate cause for a fire.

The long-term role of climate is quite diverse. Flannigan and co-authors, in their 2008 paper, summarise the importance of temperature in setting the conditions for fire:

“First, warmer temperatures will increase evapotranspiration, as the ability for the atmosphere to hold moisture increases rapidly with higher temperatures… (Roulet et al. 1992) and decreasing fuel moisture unless there are significant increases in precipitation. Second, warmer temperatures translate into more lightning activity that generally leads to increased ignitions (Price and Rind 1994). Third, warmer temperatures maylead to a lengthening of the fire season (Westerling et al. 2006).”

The importance of temperature at a global scale is demonstrated by studies suggesting that fire outbreaks have systematically increased since the last glacial maximum 21,000 years ago, when average temperatures were several degrees colder.

So once the climatic conditions set a long term likelihood for a fire to break out, as well as the distribution of tree species (and therefore the amount of fuel), short term disturbances can act to further increase susceptibility. We can divide these more immediate factors into weather, ecological, and human influences.

Unsurprisingly, weather conditions that bring hot, dry weather with the chance of thunderstorms will be highly likely to drive fires. A number of studies have shown that this kind of weather is often linked to persistent high pressure systems in the atmosphere, which push away rainfall, and can last for weeks at a time.

This kind of atmospheric conditions can often be linked to longer term weather patterns, in particular El Niño, and the effects can be long-lived. For example, El Niño brings warm, dry weather to the North-western part of North America, driving increased fire. In the South-west, El Niño brings wetter weather, but the increased vegetation growth provides a larger amount of fuel that can then burn in subsequent drier conditions.

Caption: Healthy pines mix with red, decaying trees afflicted with pine beetle infestation in Jasper National Park, Canada (Aug 2017). Credit: Robert Emberson

The growth of plants is just one way that the forest ecosystem can affect the availability of fuel for fire. Many trees are affected by pests. The classic example is the pine beetle, which can kill so many trees that whole swathes of pine forest are left characteristically red as they decay in the aftermath of an infestation. While some studies have shown that this can reduce the chance of a crown fire (since less fuel is available in the canopy), the dead and decaying trees provide a source of drier fuel at ground level that is a concern in many regions.

Elsewhere, we can see cases where trees encourage fire. Eucalyptus trees contain oil that burns strongly; the fire that this produces is suggested to remove the other tree species competing with the Eucalyptus. A strange method, but no doubt effective! The Eucalyptus, introduced to Portugal by humans in the 18th century, has been linked to many of the deadly fires that occurred there this summer. The lodgepole pine, too, has pinecones that require the heat of fire to open and release their seeds.
As such, fire is a natural part of the ecosystem, and in most areas of the boreal forest fire management is limited, with attempts at suppression only made where human settlement is at risk.

Where humans do step in, their actions can have an important role in setting the overall susceptibility to fire. Creating ‘fire breaks’ by felling or controlled burning of woodland in the path of a fire removes fuel and limits the growth of a fire, and a program of controlled burns is an important part of forest management to limit the potential for future fire by clearing scrub vegetation at the surface.

On the other hand, continual suppression of fires can lead to build up of fuel – which can then form a significantly more dangerous fire on a long term basis.

Ken Lertzman, Professor of Forest Ecology and Management at Simon Fraser University, told me that in general, control mechanisms are only useful for smaller surface fires; once the fire reaches the canopy, fire suppression is extremely difficult.

“It’s a combination of a statistical and philosophical problem”, he says. Fire control is expensive, so unless it’s financed by profits from felled lumber, cost benefit analysis is necessary, based in part on the statistical probability of a huge fire breaking out in a given location. Philosophically, though, “management forest stand structure at the boundary conditions [between surface and canopy fires] may be able to keep small fires becoming extreme.” and thus perhaps it’s worth trying to use control mechanisms even if giant canopy fires would ignore them, just to avoid that transition to the canopy.

As with most natural systems, the factors discussed above don’t necessarily act independently. Many can amplify other effects. For example, the geographical range of pine beetle outbreaks could increase under a warming climate. At a smaller scale, giant fires can create their own weather patterns, acting to dry out the surrounding forest even before it ignites. So, is the greater incidence of fire this year down to this kind of combination of factors?

What’s happening in 2017?

The sun at 10.15 in the morning in Chilliwack, BC, 3rd August 2017 – more than 50km from the nearest fire. Credit: Megan Reich.

The summer of 2017 has been brutal for wildfire in many locations. Europe has been hit hard with more fires in one day in Portugal than any previous on record. In British Columbia (BC), the largest single fire on record is currently burning, contributing to the largest total area burned in historical record. The fires released so much particulate matter and haze that the sun was obscured in large parts of BC.

According to Professor Lertzman, in British Columbia at least, this is “a fire year different in degree, not in kind”. The same processes are at play as always, but in overdrive. An early spring thaw combined with a long, hot and dry summer created the ideal antecedent conditions for fire.

Linking individual intense ‘fire years’ to long term climate change in challenging, but it is likely that these kind of conditions would be more likely to occur in a world influenced by anthropogenic climate change. Years like this one, which are clearly exceptional compared to the long term trend for fire, might begin to occur more often; every 5-10 years rather than every 30-50, for example.

In the short term, fire damage and suppression is expensive, both financially and in terms of lives affected. Smoke is a health risk to wide areas in the face of such intense fire, but ecological damage can be more difficult for humans to see.

Mature forest is a different niche for organisms to fill in comparison to fresh surfaces stripped bare by fire. While each ecosystem has its place in the natural forest, an increased prevalence of fire reduces the mature forest available for the species that prefer that ecological zone. These can range from recognisable mammal species such as bears, deer and caribou, to less well-known but still important canopy lichen species, says Professor Lertzman.

While this year’s fire season is beginning to ease off, it is clear that the range of factors, both natural and those driven by humans, will continue to play a role in years to come. More build-up of infrastructure in developed countries puts more human settlement at risk, so a clear understanding of how fire interacts with the climate, weather, and forest management strategies will be vital to allow us to live alongside fire in the future with fewer problems.

By Robert Emberson, freelance science writer


Further reading and resources