Metal detectors come in handy when looking for buried old coins. To maximize the search, you’d need a detector whose detection range extends to the average distance of buried coins from the surface. But how deep are old coins normally buried?
While old coins are sometimes buried just an inch or two (25.4 or 50.8 mm) underground, they are typically at least 6 inches (152.4 mm) beneath the topsoil. On average, you can find old coins around 6-10 inches (152.4-254 mm) underground.
If you’re interested in collecting coins, I’ll explain the various processes that lead to coins getting buried deeper and deeper into the ground. I’ll detail the conditions that determine how deep a coin gets buried in this article.
How Do Old Coins Get So Deep in the Ground?
Anthropogenic and natural forces transport coins deposited near the surface deeper underground. Most coins get buried underneath because of rain, moving soil, or other natural forces. Plus, animals can also carry coins away and bury them further underground. Then, it’s just a matter of gravity and changing landscapes pushing the coins further down.
How far underground a coin goes varies depending on location. Climate, vegetation, and foot traffic (both human and animal) are the most common factors influencing deposition depth. However, extreme weather events and geographic activities can also play significant roles.
Natural and anthropogenic forces transport coins horizontally and vertically, and their intensity and direction, in combination with the area’s characteristics, dictate how deep they are buried.
1. Erosion and Sedimentation
When erosion occurs in an area, we often notice how different the location looks and how artifacts that were previously buried deep are now found closer to the surface. What we miss, though, is where transported soil goes and how it affects that location.
As wind and water erode soils, the latter gets deposited in a new location, burying what used to be at the surface. This happens through a process called sedimentation. Erosion and deposition are geographical processes that unearth sub-surface materials in one location and cover artifacts at their deposition site.
Where sedimentation occurs, materials buried at shallow depths go deeper underground because of the excess mud and sand above them. Thus, coins that previously lay on the surface or just below end up buried underground because soil piles up in those areas.
In locations where rapid deposition of transported soil occurs, we can observe an interesting stratification of coins (along with other historical artifacts) according to their temporal classification.
An accurate time capsule is created as deposited earth materials seal the site way before new items are deposited and mixed with the earlier items. Specifically, newer you can detect newer coins close to the surface, and older ones are found deeper.
On the contrary, when the deposition rate is slow, coins collected at varying times lie on the same level once sedimentation has fully covered the layer.
Vegetation does at least two things that affect coin burial.
Firstly, it can hold the soil in place to prevent erosion, effectively preventing shallowly buried coins from surfacing. It also helps preserve the coins’ location by constraining their horizontal motion even as strong wind and water currents wash through the area.
For this reason, vegetation plays an important role in coin burial. Areas with thick vegetation are most likely capable of keeping old coins within the vicinity despite atmospheric activities such as strong winds and storms.
When soils get transported from a higher to a lower elevation during erosion, vegetation can trap these materials. As a result, coins previously lying flat in between plant stems may get covered in mud or loose soil particles. Over time, the same cycle can lead to deeper burial.
Secondly, the movement of plant roots can either uproot buried coins or push them further down into the ground. For instance, willows, whose roots extend to roughly 12 inches (304.8 mm), form a thick stronghold that can tightly pack buried artifacts and trap them until a strong enough disturbance occurs.
In regions where floods and earthquakes rarely occur, you may find coins buried even deeper than the average burial depth of 12 inches (304.8 mm). In addition to plant roots and surface growth effectively building a barrier against soil erosion, the accumulation of fallen leaves and other dead plant materials redefine what used to be surface level.
In such a case, the coins may not necessarily change their absolute location, but they are now farther from the surface on a relative scale. If left undisturbed for long periods, this plant litter will increase, burying coins much further.
3. Foot traffic
Foot traffic makes a world of difference in what happens to coins dropped on the surface or deposited near the surface. Depending on location, foot traffic may be mainly facilitated by animals such as the grazing types whose hooves quickly disperse shallowly deposited materials on the ground with every movement.
Human movement can also disperse coins in a similar way. Urbanized locations are more likely to have heavier human foot traffic. In this case, when passersby don’t pick up coins, they are more likely to move horizontally than vertically and remain at shallow depths.
This pattern contrasts with locations with mostly vegetation rather than foot traffic. Since vegetation usually buries coins and other materials over time, with minimal foot traffic, horizontal movement barely takes place, and collectors will have to dig deeper into the ground to look for coins.
In addition to erosion-sedimentation and vegetation, climate plays an important role in coin burial. Climate is the long-term atmospheric condition in an area.
Dry climates or those that receive minimal rain are less likely to result in horizontal movement due to water currents. Hence, assuming exceptionally strong winds, heavy foot traffic, or extreme geographic events frequent the area, coins are more likely to stay relatively in place with respect to their horizontal position.
Depending on other factors, such as soil permeability, coins may travel deeper into the ground or stay in place. On the other hand, when an area is generally wet, storms and floods increase the likelihood of disturbing the original position of the coins.
Combining these with other factors, like erosion and subsequent sedimentation, leads to coins moving deeper underground.
5. Soil Permeability
Soil permeability is a measure of how easy or difficult it is for materials, whether solid, liquid, or gas, to penetrate the soil. Soils with more holes or pores have higher permeability, while tightly packed soils are less permeable.
Soils rich in vegetation and constantly receiving precipitation are most likely to remain intact. This way, coins only have a little room to travel down deeper into the ground. They are also less likely to be eroded as plant roots hold them together, while stems and other plant materials hamper motion induced by wind and water.
In such cases, there is a high probability for coins to remain in the exact location, especially if minimal foot traffic and other types of disturbances occur in the area.
However, when soils are looser or more porous, coins tend to get buried deeper as less force within their surroundings keeps them in place. Loose soils make it easier for buried coins to travel deeper underground. Since such soils also erode more readily, coins found above the surface may travel horizontally due to wind or water action.
However, due to a constant flux of loose soil particles getting carried away, rapid sedimentation can counter erosion’s unearthing effect. This way, coins end up farther from the surface than they initially were.
And while on the topic of different types of soil, check out my article on what kind of grounds are most likely to have gold: Here’s What Kind of Ground You Can Find Gold In
While up to a dozen factors lead to coin burial, gravity is always a common denominator. When animals erode the topsoil with their claws or hooves, it may expose coins on the surface.
Gravity prevents coins from being transported when the wind brushes through an area unless the wind is strong enough to counter the downward vertical gravitation force.
Since gravity is virtually constant at any point on the earth’s surface, it doesn’t matter where the coin is. The force of gravity will be the same, and it will not affect how much deeper a coin will get buried. What it does, instead, is keep coins in place unless an external force acts upon them.
Another important factor affecting the depths at which coins are buried is time. Ancient coins usually require months or years of excavation to uncover because they’re often buried several meters below the surface.
They’re so hard to uncover because of the amount of time that has passed since they fell. For example, the Mohenjodaro excavation site is several meters deep and still hasn’t uncovered the entire ancient city.
Thus, truly ancient coins will likely be buried several feet or meters underground. These coins require professional excavations to uncover them.
While you can find old buried coins in a wide range of depths, a range between 6 and 10 inches (152.4 and 254 mm) is typical.
The location of the buried coins significantly affects how deep they go beneath the topsoil. Locations with heavier foot traffic constantly disturb the soil and transport the coins horizontally rather than vertically.
Meanwhile, those with thick vegetation will likely have coins buried deeper into the ground.
The main reasons coins get buried are weather conditions, foot traffic, and gravity.