Geomagnetic anomalies are variations in the Earth's magnetic field caused by differences in the magnetic properties of subsurface materials. These can be caused by natural features like iron ore deposits and faults, or by man-made objects like buried pipes, storage tanks, and even forgotten metal debris.

How to Investigate

The primary tool for this is a magnetometer. A magnetometer measures the strength of the local magnetic field. By taking measurements at various points across an area, you can create a map that highlights anomalies.

• Smartphone Magnetometer Apps: Many modern smartphones have a built-in magnetometer. You can download a free app to use this sensor. This is a great starting point for a simple, low-cost survey. It's not as sensitive as professional equipment, but it can detect large, shallow ferrous objects.

• Surveying: To get meaningful data, you need to conduct a systematic survey.

  • Create a Grid: Mark out a grid on the ground in your area of interest. Use a measuring tape or string to ensure your points are evenly spaced (e.g., every 1 to 2 meters).

  • Take Readings: Stand at each point on the grid and take a magnetic reading, holding your phone or magnetometer at a constant height and orientation. Make sure you don't have any metal objects on you (keys, belt buckles, etc.) that could interfere with the readings.

  • Record Data: Keep a log of your readings and their corresponding grid coordinates.

• Analyze the Data: Plot your data on a simple map. Areas with significantly higher or lower readings than the background are potential anomalies. A sharp spike might indicate a small, buried metal object, while a broader, more gradual change could suggest a larger geological feature.

Gravitational anomalies are variations in the Earth's gravitational field caused by differences in the density of subsurface materials. Dense materials like massive mineral deposits or igneous intrusions will cause a slight increase in gravity, resulting in a positive anomaly. Less dense materials, such as sedimentary basins, voids, or cavities, will cause a slight decrease, resulting in a negative anomaly.

How to Investigate

Investigating gravitational anomalies is more challenging for an amateur because it requires a highly sensitive instrument called a gravimeter or gravity meter. These devices are incredibly precise and expensive, making them inaccessible for most individuals. However, understanding the principle is still useful.

• Principle: A gravimeter measures the acceleration due to gravity at a specific point. To identify an anomaly, the measured value is compared to a theoretical value for that location, which accounts for factors like latitude and elevation.

• Challenges: The changes in gravity are extremely small, measured in milligals or microgals, which is why a professional gravimeter is needed. Factors like tides and local topography can also influence the readings, requiring complex corrections to get accurate data.

Alternative Approach for Amateurs

While you can't realistically perform a gravity survey, you can use existing data. Geoscientific data from government agencies or universities might be publicly available online. You can search for "gravity anomaly maps" or "geophysical surveys" for your specific region to see if any professional data has already been collected and published. This can provide valuable insight into the subsurface geology of your area without needing specialized equipment.