In late 2023, researchers confirmed that Taam Ja’, a blue hole in Chetumal Bay off Mexico’s Yucatán Peninsula, is the deepest known blue hole on Earth. Measurements taken in December 2023 recorded depths exceeding 1,372 feet without reaching the bottom.

Blue holes are underwater sinkholes that formed when ancient caves collapsed and were later flooded as sea levels rose. Unlike the famous Great Blue Hole in Belize, Taam Ja’ is nearly invisible from the surface, which is one reason it remained undetected for so long.

The site first came to researchers’ attention more than a decade ago, when a local fisherman mentioned the location to his son, who later brought it to scientists.

During the 2023 survey, researchers lowered a CTD profiler into the hole to measure conductivity, temperature, and depth. At around 1,312 feet, they observed an unexpected change: the water became warmer and saltier, with readings matching the open Caribbean Sea. That was unusual because Taam Ja’ is located far inside the bay, cut off horizontally from the open ocean.

The finding suggests the hole may be connected to the sea through subterranean tunnels or fractures in the rock. The region’s geology supports this possibility. Taam Ja’ sits near the Chicxulub crater, the site where a large asteroid struck about 66 million years ago. The impact is widely associated with the extinction of the dinosaurs, and it may have fractured the underlying rock in ways that later made cave and tunnel formation more likely.

During the first expedition, divers observed that the water above the hole was calm while the rest of the bay was choppy. At one point, water rose steadily from the center of the hole, similar to a slow spring rather than a geyser or splash.

Diving in the hole is not feasible for most people. Recreational divers are limited to about 130 feet, and even professional divers rarely exceed 1,000 feet due to extreme water pressure. Scientists plan to use remotely operated vehicles equipped with cameras and sensors to continue studying the hole.

The deeper parts of blue holes typically have very low oxygen levels, which limits the types of life that can survive there. In similar environments, scientists have found microscopic organisms such as foraminifera and nematodes. In Taam Ja’, larger marine life has not been observed even in the upper, oxygen-rich layers. Only microscopic organisms appear to be present.

There is speculation that any microbial life in the depths could be ancient and adapted to extreme conditions. Whether the hole connects to other underwater systems remains uncertain.

In other geological news, researchers at Virginia Tech conducted a study on land subsidence in the United States and found that 28 major cities are slowly sinking. The study identified widespread subsidence in cities including New York, Dallas, Seattle, and Houston.

The rate of sinking is generally a few millimeters per year. While that may sound minor, uneven sinking can create structural problems for buildings, roads, and other infrastructure over time. The study noted that more than 29,000 buildings are located in areas at risk of damage.

The primary cause of subsidence in these cities is the extraction of groundwater. As urban populations grow, authorities increasingly draw water from underground aquifers, which causes the ground above to settle. The problem is particularly severe in California and Texas.

In Jakarta, Indonesia, land subsidence has been so severe that the country is moving its capital to a new city called Nusantara, which is being designed to absorb rainwater rather than let it flood streets. Experts estimate that much of North Jakarta could be submerged by 2050.

Scientists have proposed several solutions to slow subsidence, including recycling wastewater and harvesting rainwater to reduce dependence on underground sources.

The Gulf of Mexico, although technically a gulf, behaves in many ways like an independent ocean system. It is semi-enclosed, unusually deep in places, and located in the tropics, where it absorbs and stores large amounts of solar heat. Warm eddies deep beneath the surface can intensify hurricanes passing through the region.

The Gulf also feeds the Gulf Stream, which carries warm water across the Atlantic and helps keep Western Europe milder than its latitude would normally allow. The region supports significant economic activity, including offshore oil and gas production and reef tourism.

In 2010, the Deepwater Horizon disaster released about 4.9 million barrels of oil over three months, the largest accidental marine spill in petroleum history. Around 27,000 abandoned oil and gas wells lie beneath Gulf waters, many of them poorly monitored.

New York City has also been the subject of subsidence research. A study calculated the total mass of the city’s buildings at more than 1.68 trillion pounds and found that the city is sinking at a rate of about 0.04 to 0.07 inches per year. Certain types of soil, including clay and artificial fill, are more prone to sinking than bedrock.

Similar issues affect other coastal cities. Venice continues to sink slowly, partly due to sediment compaction and groundwater extraction, and partly because tectonic activity is tilting the area. The city’s historic buildings are increasingly exposed to saltwater damage.

New Orleans was built on soft, swampy ground. A drainage system installed in the early 1900s removed water from the soil, causing former marshlands to sink. By the time Hurricane Katrina arrived in 2005, around half the city was below sea level.

In Hawaii, parts of Oahu are sinking at rates that could increase flood risk significantly by 2050. The islands are gradually cooling and subsiding as they move away from the volcanic hotspot that created them, and some coastal areas built on artificial fill are sinking faster than the rest.

Miami Beach also faces subsidence issues. Satellite data collected between 2016 and 2023 showed that at least 35 high-rise buildings on the barrier island had moved downward, with some dropping nearly three inches. The ground beneath the island consists of sand and limestone that can shift under heavy, sustained weight. Construction activity and water moving through the porous rock may also contribute to the movement.

The findings do not mean the buildings are unsafe, but they serve as an early warning signal for engineers.

In China, a team of scientists is drilling a borehole in the Taklamakan Desert with the goal of reaching nearly 33,000 feet, more than one and a half times deeper than Mount Everest is tall. The project is intended to explore the Earth’s internal structure, search for mineral and oil deposits, and gather data on earthquakes and volcanic activity.

The deepest man-made hole on Earth remains the Kola Superdeep Borehole in Russia, which reached a depth of about 40,000 feet before the project was abandoned in 1995. Drilling stopped because temperatures at the bottom, around 356 degrees Fahrenheit, were twice what scientists had expected, and the rock behaved more like plastic than solid stone.

Scientists have not given up on drilling deeper. A Japanese research ship called Chikyu was built about 20 years ago to drill into the ocean floor, where the Earth’s crust is thinner. The mission’s goal is to recover mantle rock for the first time.

Sinkholes continue to appear in various parts of the world, both naturally and because of human activity. In 2020, a sinkhole in Queens, New York, swallowed an SUV overnight. In China, explorers discovered a large sinkhole in Guangxi that contained an ancient forest with trees reaching heights that suggest the ecosystem has been undisturbed for a very long time. The region is known for karst topography, which forms when rainwater dissolves limestone over thousands of years.

A sinkhole in Kuala Lumpur swallowed a pedestrian in 2024, and a second hole opened nearby days later. In Naples, a sinkhole opened on a quiet street and swallowed two cars, one of which had passengers who escaped with minor injuries.

Florida is especially vulnerable to sinkholes because much of the state’s ground is made of porous limestone that erodes easily. In 2013, a sinkhole in Hillsborough County opened beneath a home and claimed the life of a resident. The county later purchased the property, and the hole reopened twice more without causing further injuries.

Geologists use ground-penetrating radar to detect underground cavities before they collapse. Stabilization methods include filling the holes with cement or polyurethane foam and driving steel rods into deeper, load-bearing soil.