How much sand do we have left? New transport equations for carbonate deposits

A new study provides insights and suggests new models on carbonate sand deposits movements. The study can shed light on the total amount of sand deposits that are left on earth.

Sand is a soil material that consists of rock minerals or small blocks. It forms from gradual erosion and weathering of rock materials that are transferred through rivers and finally reach the sea where they are further eroded due to wave action.

The most common type of sands is silica sands that contain quartz, a mineral found in rocks that is highly resistant to weathering. However, there are many more types of sands such as carbonate sands, volcanic sands, or greensands. 

Quantifying the remaining sand deposits on earth is crucial given that sand is widely used in construction and other industries. In fact, it is the second most extracted deposit worldwide after fossil fuels. According to a report issued in 2019 in Nature, sand and gravel are being extracted at rates much higher than they are deposited, a fact that is partially caused by illegal mining activities.

Scientists from the Cyprus International University, the University of Sydney and the Eastern Mediterranean University collaborated to create more accurate models of measuring sand resources. Their findings were published in the Journal Scientific Reports by Nature.

Prediction models of sand deposits were created based on certain assumptions that derive from previous experimental data. One of those assumptions is that the sand grains are spherical, a fact that is generally accepted considering quartz sands. However, carbonate sands (which mainly consist of carbonate minerals) have an elliptical shape and larger porosity, thus, the current models cannot accurately predict their quantities and their spatial movement. “Not all sand is the same. Yet the models for assessing sand and how it moves mostly rely on one type. This means we have an inaccurate picture of what is happening, especially in coastal areas..." Ana Vila-Concejo, co-author of the study and an Associate Professor at the School of Geosciences, University of Sydney, stated.

The research team conducted experimental tests on carbonate sands to understand their behavior and derive mathematic models describing their mass movement. Moreover, they applied the derived models on data collected over a 6-year period on carbonate sand movements in Hawaii.

According to the results of the study, the outdated models used to overestimate the movement of carbonate sands on the seafloor by more than 20% while underestimating their suspended transport (the motion of the sand particles through the water) by more than 10%. “This means we are not accounting for sand correctly,” Prof. Vila-Concejo added.

Researchers agree that correctly predicting the movement of sand sediments is crucial in an era when climate change and sea level rise might affect a large portion of the coastal areas with sand deposits on the planet.