Don’t Get Sunk: Everything You Need to Know About Sinkholes (Part One)

Photo by Steven Reilly/New Jersey Herald

Sinkholes are a phenomenon that tend to baffle and frighten most people. How is it possible that the ground beneath our feet could just drop? How do we know if we’re nearby a sinkhole? What should we do if we see one? How are sinkholes fixed? The mystery of the unknown around sinkholes can be quite unnerving.

Have no fear, we’ve got answers to all of those questions and more! In this two-part blog series, our experts share their knowledge and provide important information about this scary occurrence. In part one, we provide a detailed look at what a sinkhole is, three different types of sinkholes, and what causes them to form. In part two, we explore how to detect sinkholes and the steps taken to repair them.

What is a Sinkhole?

Sinkholes are a common phenomenon around the world. They result from both man-made and natural causes. Marshall Thomas, a Princeton Hydro geologist, describes sinkholes as “depressions observed from the surface, caused by dissolution of carbonate rocks.” In other words, sinkholes form when the rock below the land surface gets dissolved by water that penetrates the surface and continues to move downward, further into the subsurface.

Most common in areas with “karst terrain,” or types of rocks that can easily be dissolved by groundwater, sinkholes can go undetected for years until the space underneath the surface gets too big or enough of the surface soil is washed away. Sometimes the holes are small, measuring a few feet wide and ten feet deep. Sometimes the holes are hundreds of miles wide and deep. However, all of them can be dangerous.

Sinkholes are found throughout the world. States like Pennsylvania, Texas, Florida, Alabama, Tennessee, and Missouri are at higher risk for sinkholes because they tend to have more soluble rocks like salt beds and domes, gypsum, limestone, and other carbonate rocks. People living in these states are recommended to have professionals look at any property they intend to buy to make sure it isn’t in an area above soluble rock.

Types of Sinkholes

Not all sinkholes are the scary, earth-falling-out-from-underneath-your-feet events. Some occur slowly over time and are very evident from the surface. Geologists classify sinkholes in three major types. Their formation is determined by the same geological processes, barring a few differences. Let’s dive in!

1. Dissolution Sinkholes

Illustration by USGSDissolution sinkholes start to form when limestone or dolomite is very close to the soil surface, usually covered by a thin layer of soil and permeable sand which washes away or is eroded. Rain and stormwater runoff gradually percolate through crevices in the rock, dissolving it. Consequently, a bowl-shaped depression slowly forms.

Sometimes, dissolution sinkholes become ponds when the depression gets lined with debris, which traps water inside. Dissolution sinkholes develop gradually and are normally not dangerous. However, the ones that become ponds can drain abruptly if water breaks through the protective bottom layer.

Fun fact: Most of Florida’s lakes are actually just large sinkholes that filled up with water!

2. Cover-Subsidence Sinkholes

Illustration by USGSThis type of sinkhole, which starts with the dissolution of the underlying carbonate bedrock, occurs where the covering sediment is permeable (water can pass through it) and contains sand. First, small pieces of sediment split into smaller pieces and fall into openings in the carbonate rock underneath the surface. With time, in a process called piping, the small particles settle into the open spaces. This continues, eventually forming a dip in the surface ranging from one inch to several feet in depth and diameter. Again, these aren’t the sinkholes movies are made about.

3. Cover-Collapse Sinkholes

Illustration by USGSThis type of sinkhole is the one making headlines and causing fear. In order for cover-collapse sinkholes to happen, the covering soil has to be cohesive, contain a lot of clay and the bedrock has to be carbonate. Similar to the cover-subsidence sinkholes, the cohesive soil erodes into a cavity in the bedrock. The difference with this is that the clay-filled top surface appears to remain intact from above. However, underneath, a hollowed out, upside down bowl shape forms. That hollowing gets bigger and bigger over time until eventually, the cavity reaches the ground surface, causing the sudden and dramatic collapse of the ground. Just like that, poof, we have a sinkhole that appears to be surprising and abrupt but really has been brewing for many years.

What Causes a Sinkhole?

Sinkholes can be natural or man-made. The most common causes of a sinkhole are changes in groundwater levels or a sudden increase in surface water.

Intensive rain events can increase the likelihood of a sinkhole collapse. Alternatively, drought, which  causes groundwater levels to significantly decrease, can also lead to a greater risk of collapse of the ground above. In a world with a greater variability in rainfall and drought events due to climate change, sinkholes may become a more common occurrence around the world.

Humans are also responsible for the formation of sinkholes. Activities like drilling, mining, construction, broken water or drain pipes, improperly compacted soil after excavation work, or even significantly heavy traffic (heavy weight on soft soil) can result in small to large sinkholes. Water from broken pipes can penetrate through mud and rocks and erode the ground underneath and cause sinkholes.

Most commonly, human-caused sinkholes are the result of:

  • Land-use practices like groundwater pumping, construction, and development
  • Changing of natural water-drainage patterns
  • Development of new water-diversion systems
  • Major land surface changes, causing substantial weight changes

In some cases, human-induced sinkholes occur when an already forming sinkhole is encountered during construction processes such as excavation for stormwater basins and foundations. Dissolution of bedrock generally occurs in geologic time-frames (thousands of years). In these cases, the excavation process has removed the covering soils, decreasing the distance between the top of the void and the ground surface.  

In other cases, voids in the bedrock are generated due to rock removal processes such as hammering and blasting. Hammering and blasting can generate fractures or cracks in the bedrock that soil can then erode into. A void in the bedrock may already exist, however, the process of removing the bedrock by hammering and/or blasting can speed up the meeting of the upside-down bowl and the surface that much quicker. One site where this happened has experienced over 35 sinkholes in 4 years.

Overall, it’s generally not a good idea to pump groundwater or do major excavation in areas that are prone to sinkholes. According to the USGS, over the last 15 years sinkhole damages have cost on average at least $300 million per year. Because there is no national tracking of sinkhole damage costs, this estimate is probably much lower than the actual cost. Being more mindful about the subsurface around us and our actions could help lower the average yearly cost in damages and even save lives.

Photo by Barbara Miller PennLive Patriot News

Stay tuned for Part Two of this blog series in which we explore we explore how to detect sinkholes and the steps taken to repair them! For more information about Princeton Hydro’s Geotechnical Engineering services, go here: http://bit.ly/PHGeotech

Special thanks to Princeton Hydro Staff Engineer Stephen Duda, Geologist Marshall Thomas, and Communications Intern Rebecca Burrell for their assistance in developing this blog series.

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A Scientist’s Journey to the Antarctic: A Princeton Hydro Blog Series

This two-part blog series takes us on an adventure to the southernmost continent and explores how changes to Antarctica’s ecosystem have worldwide impacts.

Welcome to Part Two: The Continent of Science

Antarctica, the most remote and inaccessible continent in the world, is also, on average, the coldest, windiest and driest continent. Quick Fact: Antarctica is actually a desert! Additionally, with an average elevation of about 7,200 feet above sea level, it is also the world’s highest continent.

There are no native people in Antarctica, but scientists from all over the world visit the continent to conduct research. During the summer, approximately 4,000 scientists visit “the continent of science” to carry out research in a wide range of physical and biological sciences – from the vastness of space to the minutest scale of microorganisms. The research conducted here has helped to highlight global problems, including climate change.

Tourists also visit Antarctica during the summer to enjoy the spectacular scenery and abundant wildlife. In Part One of our two-part blog series, we take you on an Antarctic journey through Sophie Breitbart’s experience aboard the National Geographic Explorer ship. Sophie saw a variety of wildlife during her 10-day educational excursion, including Crabeater and Leopard seals, gentoo and Chinstrap Penguins, Humpback and Killer whales, migrating Red Knots, and more.

Polar tours like the National Geographic Lindblad Expedition help to raise climate change awareness and create lifelong wildlife ambassadors, and the profits from responsibly managed tourism help to fund critical scientific expeditions to the Antarctic.

Just last year, a research mission conducted by the National Oceanic and Atmospheric Administration discovered that sea ice cover in the Antarctic is near record lows – 18.2%, or 520,000 square miles, below the 1981-2010 average. That is the second lowest sea ice report since record-keeping began in 1979, with the first being recorded in 2016. Smaller ice shelves in the Antarctic Peninsula are currently retreating, breaking up into vast fields of icebergs, likely due to rising temperature and surface melting.

Snow and ice make up more than 95% of Antarctica’s surface terrain. The continental ice sheet contains approximately seven million cubic miles of ice, representing about 90% of the world’s total ice. The average thickness is about 1.5 miles. To understand its extent, if Antarctica’s ice were to melt today, global sea levels could rise 150 – 200 feet. It’s massive.

Climate change impacts are already being documented in Antarctica. The Antarctic Peninsula’s glaciers have been warming faster than the rest of the continent. As the snow and ice decrease, the land cover increases and absorbs more heat, which in turn increases the rate of warming. In 2017, a study published in Current Biology found that over last 50 years, temperatures have been rising, and therefore have caused a steady growth of moss on the continent.  So, scientists are now predicting that, “terrestrial ecosystems will alter rapidly under future warming, leading to major changes in the biology and landscape of this iconic region—an Antarctic greening to parallel well-established observations in the Arctic.”  And, another study by researcher Bill Fraser has reported that Adélie Penguin populations have decreased from 32,000 breeding pairs to 11,000 in 30 years because of the changes in temperature.

Changes to the global sea ice cover reported by NOAA not only carry major implications for the continent of Antarctica, but for the entire world. 97% of actively publishing climate scientists agree that earth’s climate is warming, and the evidence that the Arctic’s ice caps are melting at an accelerated rate due to climate change is blaring. And, more than 62% of Americans say they are at least “somewhat worried” about global warming. Yet, not many people are taking daily actions to slow global climate change.

We must make every effort we can to limit our own carbon footprint and mitigate climate change. It has been said that there are most likely no greater ambassadors for Antarctica than the tourists who have been there and return home to share information about the need for its protection.

When Sophie returned from her trip, she said “I became an environmental scientist because I have a passion to conserve biodiversity. Being immersed in this wild place and experiencing firsthand the magnificent yet fragile Antarctic landscape acts as a reminder of why it’s so important to do this work. Those memories inspire me to keep at it.”

To learn more about Antarctica and what scientists with World Wildlife Fund are doing to protect it, go here. If you have any questions for Sophie about her journey, please email us or comment below.

 

Sophie Breitbart worked for Princeton Hydro from March 2016 until May 2018, first as an intern and then as a staff scientist. She is now pursuing her PhD in Ecology and Evolutionary Biology at the University of Toronto, where she will study how urban development affects the ecology and evolution of interactions between the plant common milkweed, its herbivores, and pollinators.

 

A Scientist’s Journey to the Antarctic: A Princeton Hydro Blog Series

A trip to Antarctica has long been at the top of the bucket list for Sophie Breitbart, former Staff Scientist at Princeton Hydro, and her father. Ultimately inspired by the extraordinary spirit of adventure in “South: The Endurance Expedition,” the story of British explorer Ernest Shackleton‘s 1914 attempt to reach the South Pole, the two decided that it was time to make the journey to the white continent. What they experienced was far more than a travel dream fulfilled.

This two-part blog series takes us on an adventure to the southernmost continent and explores how changes to Antarctica’s ecosystem have worldwide impacts.

Part One: Antarctic Adventure

The National Geographic Lindblad Expedition trip began with a flight to Buenos Aires, Argentina, where Sophie and her father met up with the other travelers and an expedition crew that consisted of an exploration leader, eight veteran naturalists, a National Geographic photographer, a Lindblad-National Geographic certified photo instructor, an undersea specialist, a Global Perspectives guest speaker, and a video chronicler.

Ushuaia, Argentina

In Buenos Aires, the group, totaling approximately 140 people, boarded a private charter flight to Ushuaia, Argentina, the world’s southernmost city. After taking in views of the Martial Mountains and the Beagle Channel, which is commonly referred to as The End of the World, the group climbed aboard the National Geographic Explorer ship and set sail for a 10-day Antarctic adventure.

The National Geographic Explorer is a 367-foot expedition ship that accommodates 148 guests in 81 cabins. The Explorer is uniquely equipped with an ice-strengthened hull, advanced navigation equipment, a variety of exploration tools, and vast expanses of windows that provided the ultimate vantage point for spotting dolphins and sea birds as the ship left the Beagle Channel.

Before reaching the Antarctic, the ship would have to pass through the infamous Drake Passage, the body of water between Cape Horn in South America and the South Shetland Islands in Antarctica, where the Atlantic, Pacific, and Southern seas converge. Because the currents in the Passage meet no resistance from any nearby landmass, they can be some of the choppiest waters in the world. Luckily for Sophie and the other Explorer travelers, the Drake Passage was cooperative for the most part and the journey through it was relatively smooth. (Editor’s Note: The journey back was another story.)

On day five of the journey, the ship arrived in the Antarctic Peninsula.

“The ice was so shocking and jaw-dropping,” said Sophie reflecting on her first impression of Antarctica. “I had never seen anything like it before. There were so many different shades of blues and whites and countless textures. It was truly incredible to see.”

With close to 24 hours of daylight, the exploration opportunities were endless. Sophie and her father participated in kayaking tours, expeditions on an 8-person zodiac boat, around the clock wildlife watching, and even a few hikes on the Antarctic Peninsula. There they saw indigenous rocks and artifacts, remnants of British research stations from the 1950s, and lots of wildlife, including nesting South Polar Skua Birds, penguins swimming and jumping out of the water, and a playful group of Leopard Seals.

Humpback and Killer whales skirted the ship as well. A Killer Whale research team aboard the Explorer took blow samples, which would be genetically sequenced, and shared  with passengers their aerial imagery findings, which they captured in order to record the whales’ dimensions, family structures, and health. Sophie and her father enjoyed a variety of whale sightings. During one of their kayaking expeditions, a large Humpback Whale surfaced just 10 feet away from them, then swam right underneath the kayaks and resurfaced, showing lots of playfulness and curiosity.

Check out this incredible video showing a fascinating strategy that killer whales use to hunt seals:

While Sophie struggled to choose a favorite moment from the trip, she quickly recalled the memory of kayaking along the coast of the Antarctic Peninsula among a field of stunning icebergs. “They each possess a unique mixture of color, density, shape, and size… like pieces of artwork, truly breathtaking in their composition and enormity.” Another easy highlight: “One day, the captain lodged our ship into an ice floe and we had a cookout complete with BBQ and lawn chairs. Definitely a once-in-a-lifetime experience.”

Sophie described this journey as the “most amazing scientific field trip” she’s ever been on. It left her feeling inspired to continue her work as an environmental scientist and acted as a reminder about why it’s so important to continue to be involved with projects that conserve biodiversity and protect water resources.

Check out Part Two of this Princeton Hydro blog series.

 

Sophie Breitbart worked for Princeton Hydro from March 2016 until May 2018, first as an intern and then as a staff scientist. She is now pursuing her PhD in Ecology and Evolutionary Biology at the University of Toronto, where she will study how urban development affects the ecology and evolution of interactions between the plant common milkweed, its herbivores, and pollinators.