Miami-Dade County in Florida: Geological History


Geology is a natural science which studies soil and its composition, including rocks and minerals. It focuses strongly on the transformation of the Earth’s geology over the 4.5 billion years of its existence as it underwent a continuous change and cataclysmic events, which have formed the composition of the soil today. Geology has a profound impact on human civilization as society cultivates, builds on, and extracts natural resources from the soil. This report focuses on investigating the geological history of Miami-Dade County in Florida and its impact on various human activities.

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Geological Context and Features

Sea levels have played a critical role in the formation of Florida’s geological profile. The state’s topography and surficial sediments formed during levels of high sea levels as current eroded formations and shaped the landform. Underneath the water, Florida acted as a shelf for marine lifeforms. During variations of sea levels over epochs, calcium carbonate remains began to form a sedimentary limestone bedrock layer.

Southern Florida, along with the Miami area, formed its physiographic and topographic features as a combination of depositional and erosional processes. Erosion creates karst development which leads to the formation of limestone rocks. As a result of millennia of geological changes, unique subsurface features such as sinkholes and vertical shafts begin to create an underground drainage system and caves. Many of the sediments seen in Florida’s geological profile, such as quartz sand and heavy minerals, were carried by water sources from the Appalachian Mountains and coastal plains (Allen and Main).

Limestone found in the Miami area has a unique characteristic of being covered with a dense red crust called caliche, with the color being a sign of rich iron composition. The layer of limestone underneath Miami-Dade County is known as the Miami Oolite Formation. It has two distinctive facies which are representative of various depositional conditions. The Oolitic facies is a type of limestone that consists of small grains compounded together, also known as grainstone.

These elements are spherical in shape and have concrete layers around a quartz grain nucleus. Meanwhile, Bryozoan facies are encrusted organisms often seen in marine environments. These elements make up only a small portion of a limestone composition and are created by cross-bedding, water flow that buries organisms into the sediment in a process known as bioturbation (“Overview of South Florida Geology”).

Effect on the Population

The soil composition of Miami-Dade County, consisting of limestone and quartz, plays a role in urban development. The composition can affect soil strength and degradation that must be considered as a factor of safety during construction. This impacts the construction of foundations, roadways, utilities, and miscellaneous structures. Excavations of near-surface materials will not hold vertical structures for prolonged periods of time as sand layers become loose and begin to collapse due to exposure to elements.

Roads and walkway areas should be built with flexible pavement subgrade with unique specifications for compaction and stabilization. Foundational support should be constructed within the range of allowable axial capacities which can withstand resistance to lateral loads (Dueno 3). Overall, construction becomes a complex endeavor in a type of soil that is prone to degradation and instability. Miami has a significant real estate and construction market which makes the geological analysis of the area crucial to ensure the safety and sustainability of structures.

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Florida as a state and especially the Miami-Dade area has a developed industry of mineral resource extraction. Florida has an abundant amount of phosphate, which is commonly used in fertilizer and explosives. It was discovered in the late 19th-century and became a prominent industry by the 20th century. In the modern-day, Florida provides more than 80% of phosphate used in the United States and 25% of global exports (“The Mineral Industry of Florida”).

The limestone layer in Florida is considered one of the highest quality, used in the manufacturing of concrete and clinker for cement. These are used for construction and asphalt production. Miami-Dade limestone industry creates more than 14,000 jobs and $550 million in annual revenue. The limestone quarries are used for environmental protection by acting as water storage areas to protect urban areas from flooding coming from Western Everglades (“Facts about the Florida and Miami-Dade Limestone Industry”).

Geology plays a significant role in the agricultural development of society. Miami-Dade County has two major soil types which are used for agriculture and crop growth: rock land at Miami Ridge and marl soils located in former marsh areas in the southeast. Both types of land consist of porous limestone bedrocks and are alkaline with a pH ranging from 7.5-8.5. They are both low in organic matter and nutrients, requiring commercial fertilizer to raise crops.

The rock layer is well-drained with a gravelly loam surface layer that requires frequent irrigation. Winter vegetables are grown on rocky soil above sea level and require tedious cultivation by breaking it up into smaller particles. This made vegetable farming in the area impractical until the use of tractor clearing in the 1920s. Meanwhile, marl soil is denser and can be affected by flooding. It must be appropriately contoured to ensure the drainage of water. This soil can grow any type of vegetation as long as it is protected from flooding. Root crops and tree nurseries are most commonly grown on marl soil (Degner 6-7).

Immediate Impact

Miami’s geological composition makes it particularly vulnerable to climate change. Sea levels have been stably rising, with an increase of 10 inches since the 19th century as industrial practices cause global warming. However, it poses a significant risk of flooding to Miami, many of its neighborhoods located in coastal areas. Miami-Dade County, with the megapolis and surrounding satellite communities, is located on a dome-shaped foundation of porous limestone.

As sea levels rise, the limestone soaks in the water and accumulates within the foundation of the city. In turn, it begins to affect the urban infrastructure of drainage and pipes. Water pressure pushes sewage upwards, contaminating freshwater sources. The topography of the Miami area contributes to the issue as most land is located no more than six feet above sea level (McKie).

As groundwater seeps in due to the porous structure of the limestone, the effect of floods, storms, and tides is exponentially higher. Water literally begins to erupt from the ground and floods the roads. Annual autumn tides, which are extraordinarily potent, overpower any seawalls or barriers in place to protect the city. With each year, the situation becomes more prevalent and critical. This causes great concern for the real estate market, which is valued at billions of dollars in Miami alone.

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Over the next decade, the market will experience climate gentrification. People will seek to avoid settling near coastal areas, and migration patterns will exacerbate the crisis of rising sea levels (Bolstad). As evident, geology is closely related to other natural sciences such as the study of climate change and can have significant consequences for the development of human urban centers.


It is evident that Miami-Dade County and Florida as a state have a rich geological history. The contexts and features identified in this report form a unique geological profile. Using this information, patterns of land development and usage for various means can be identified. Furthermore, geological contexts are helpful to evaluate the current risks approaching Miami in the midst of climate change.

Works Cited

Allen, Ginger, and Martin Main. Florida’s Geological History. n.d. Web.

Bolstad, Erika. “High Ground Is Becoming Hot Property as Sea Level Rises.Scientific American. 2017. Web.

Degner, Robert, et al. Miami-Dade County Agricultural Land Retention Study. 2002. Web.

Dueno, Peter. Final Report of Subsurface Exploration & Geotechnical Engineering Study Proposed Douglas Park Improvements. 2015. Web.

Facts About the Florida and Miami-Dade Limestone Industry.White Rock Quarries, 2006. Web.

McKie, Robin. “Miami, The Great World City, Is Drowning While the Powers That Be Look Away.The Guardian. 2014. Web.

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“Overview of South Florida Geology.” Florida International University, n.d. Web.

“The Mineral Industry of Florida.” United States Geological Survey, 2011. Web.

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