ground fissure

Sometimes the earth splits open for no apparent reason. It’s pretty frightening to witness giant, miles-long ground cracks that makes the surface feel unstable and we humans feel rather small and vulnerable to be swallowed up by the ground. Many “mysterious earth” websites and those who believe that the End Times are upon us will focus on these earth fissures as if they are unprecedented, unexplainable, and worthy of panic and prayers.

Not quite. An example of a ground crack scaring the bejeezus out of people was a giant fissure reported in Arizona by LiveScience and Science Alert. The opening in the soil was up to 3m across, 25-30 ft deep and 2 miles long, not too shabby. A drone dramatically traced it from the air.

While this particular ground fissure was formed in 2013-2014, it got attention from sensationalist outlets like Daily Mail, (Signs of the Times) and Coast to Coast AM because it’s scary and feeds into the narrative they promote, earth fissures unrelated to seismicity are rather common. In fact, the Arizona Geological Survey monitor 26 areas mostly in Central Arizona where 170 miles of fissures are mapped. Why here? Well, the cause is pretty clear: people have overpumped the aquifers and now the ground is compacting and sinking. Fissures have been noted here since the late 70s related to extensive groundwater withdrawals in the Sonoran desert. The only water available in the desert for irrigation is deep wells. Fissures were first noted near Eloy in 1929. Officials here call it “groundwater mining” because of the removal of so much of the commodity.

Arizona has a “fissure hotline” to report new ground cracks because they pose serious hazards to livestock and off-road travelers in particular. They are particularly dangerous during and after heavy rain when the flow washes in the sides and creates a trap of mud. In 2007, a horse died in Arizona after being trapped in a muddy gouge. Rain will also cause differential settling in clayey material.

ground fissure
A map showing known earth fissures in Central Arizona.

A great piece here describes how these fissures were not a problem 200 years ago but are common today as we use groundwater faster than it can be replenished. The cracks often appear parallel to edges of bedrock that are more stable.

ground fissure
Credit C. Wanamaker

In other Western states like Utah, and in Mexico, the ground cracks are sometimes thought to be fault-related. Instead, the fissures are a visible manifestation of the ground subsidence as a result of a water table depleted by 100 feet or more causing damage to buildings, roads, bridges and railroads. According to the Land Subsidence and Earth Fissures in Cedar Valley (Utah Geological Survey),  the ground subsides several feet but moves only inches a year. Cedar Valley land dropped 2.4 inches per year. Continued groundwater pumping will only exacerbate the hazard.

In 2014, several outlets repeated a story of an “apocalyptic” crack in Hermosillo, Mexico, that many feared was related to movement on the San Andreas fault. Careful examination showed that this desert area had nearby irrigated fields suggesting that, once again, groundwater over withdrawal from arid areas was the likely culprit.

Not all earth fissures are related to subsidence. Some rare ones are due to upheaval, like this limestone bulge that very loudly occurred in 2010 in Michigan, uprooting trees. The 360 ft long, 5 ft deep and up to 30ft wide crack resulted from a violent break in the surface resulting from “popping up” of the near surface rock layers due to unloading of pressure. Again, this was not fault-related.

So, the earth will sometimes split open unexpectedly and, understandably, freaking out the nearby farmers and townspeople. But the geologists know there is probably a good reason for it. Instead of assuming it’s the beginning of the end of the world, they seek out the natural reasons, reasons that sometimes we humans had a hand in bringing about.

Ground fissures in Saudi Arabia

March 7, 2018. Dramatic and scary earth fissures unrelated to earthquakes are rather common around the world, especially in arid areas. Where the surface material is void of vegetation and organic matter but contains some clay, dry conditions may result in fissures (similar to how mud cracks). This surface cracking can be extensive and deep when associated with subsidence.

In this desert environment, it occurs in response to groundwater pumping. Pulling out huge volumes of water from unconsolidated sediments (such as sand aquifers) results in compaction, which translates on the surface as wide-scale sinking and visible fractures or tension cracks.

To those not familiar with ground fissures due to subsidence or extraction, the appearance of these huge cracks in the earth is mysterious and alarming. The latest ground fissuring incident making the rounds on “Apocalyptic” and “earth changes” websites is in the Tamir province of central Saudi Arabia north of Riyadh. The phenomenon was filmed and uploaded to YouTube by several people.

This video shows the deep fissure in loose, clayey sand. The walls easily collapse further when disturbed. The information provided roughly translates to say that the crack divides the populated area, terrifying some of the inhabitants, who are demanding the “rare” event be studied.

A February 28, 2018 video titled “Deep ground cracks north of Riyadh today” showed the location as near the village of Al Majma’ah northwest of Riyadh. The description also noted that the phenomenon was “strange” and the opening extended approximately 28 km. Local officials were looking into the events.

Although translating and searching in Arabic is difficult, there was a suggestion that the cracks became large and noticeable after a recent rain event. In the videos, you can see darker areas that appear moist suggesting that the rain widened a smaller fracture. A check of the weather at the airport in Riyadh showed a thunderstorm passed through on February 24 with rain into the early morning of the next day. No other rain was noted in February.

Such ground fracturing is not, in fact, “rare” in Saudi Arabia and it has been studied before. These studies show that fractures are linked to the amount of groundwater extracted by human settlements. It could be that the locals have not had these fractures appear in this area but that the aquifer is being depleted locally or even from miles away. A study of the local aquifer in Riyadh (Al-Jallal, I.A., 1979, “Hydrogeology of the Minjur Aquifer in the Riyadh Region of Saudi Arabia”)  described additional well fields for public and private uses were being installed in the late 1970’s but that the sandstone aquifer was exploited in the area since the mid-1950s. Riyadh is the capital of the country, with a population of more than 6 million people.

Exploitation of wells producing from the Minjur Sandstone beneath Riyadh was begun in 1956, when the first well was drilled. Since then the number of wells has increased as has the production. Production started with 35 l/sec in 1956-57 from the Shumaisi Well and was increased gradually to a total of 45 l/sec for two wells. In 1958, the production was 105 l/sec, over 600 l/sec in 1967 and more than 900 l/sec in 1971. There is almost a yearly increase in water requirements by people in the city as a result of the increase in the rate of growth. The production increased as the number of productive wells increased.

Such growth could not be sustained in the slowly-recharged aquifers and much of the water (~50%) now comes from desalination of Persian Gulf waters. The people overused water for wasteful agriculture practices and high general consumption. A serious shortage of water is projected for the coming decades.

Appearance of mud suggests a rain event enlarged the fracture. (YouTube)

The sensible conclusion is that these fissures were the result of groundwater depletion. While the locals may not have noticed them before, the situation suggests they should get used to seeing them appear. It might be a frightening future indeed if technology can’t solve the problem of providing available water to central Saudi Arabia. The earth has given all it can.

The Grand Kenyan – A huge fissure in the East African Rift valley

A huge fissure developed in the East African Rift Valley in Kenya on March 19, 2018. From Daily Nation/JAMES KAHONGEH on March 20, 2018:

At the intersection of the damage with the busy Maai Mahiu-Narok road, what was recently an even plain of fertile, arable land has been reduced to a rugged expanse, with a huge tear that is as much as 50 feet deep and more than 20 metres wide running through it.

This spot, however, is just one of the tens, perhaps hundreds, of other weak spots on the Great Rift Valley, which runs through the continent from the Horn of Africa to Mozambique, scientists say.

Families living near the fissure started moving out yesterday, with 72-year-old Mary Wambui saying “staying here is like courting death”.

She was having dinner with the rest of the family on Monday when the Earth suddenly cracked beneath their feet, cutting their home into two.

Activity here has been going on for several million years. It’s not a new discovery. But it is a complex system. The East African Rift Valley is splitting off the horn of Africa due to the upwelling of magma from the mantle. The area has active volcanoes as well as frequent earthquakes.

The cause of this particular crack is debated by scientists as some say it may be a surface reflection of a deep-seated structural fault while others say it was caused by rains.

From Lucia Perez Diaz at The Conversation:

Initially, the appearance of the crack was linked to tectonic activity along the East African Rift. But although geologists now think that this feature is most likely an erosional gully, questions remain as to why it has formed in the location that it did and whether its appearance is at all connected to the ongoing East African Rift. For example, the crack could be the result of the erosion of soft soils infilling an old rift-related fault.

Rifts just don’t “split a continent in two” overnight. There isn’t one big crack down the middle and everything falls apart. But that is what the headlines of many news stories suggested to casual readers. The split is expected on a time scale of millions of years. Meanwhile, people living in the Valley need to be watchful of surface fissures, especially during rains. And, authorities must take into account faults and geological hazards when building infrastructure.

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