Understanding Virtual Geomagnetic Poles
A virtual geomagnetic pole, often called a VGP, describes the pole position implied by one paleomagnetic direction at one sampling site. It is not always the same as the long term geographic pole. It is a useful way to compare rocks, cores, lavas, sediments, and laboratory directions on a common globe.
Why the Result Matters
Paleomagnetic directions record declination and inclination. Declination shows the horizontal angle from north. Inclination shows the dip below or above the horizontal plane. When those values are paired with site latitude and longitude, the calculator converts the local direction into a pole latitude and pole longitude. This helps researchers test apparent polar wander, plate rotation, reversal behavior, and data consistency.
Inputs and Interpretation
Accurate site coordinates are important. Small coordinate errors can move the calculated pole. Declination should be corrected for bedding tilt, orientation bias, and local reference choices before use. Inclination should use the final accepted direction. Reverse polarity directions can be converted to their normal antipode when the option is selected. The alpha ninety five field is optional. It gives a simple confidence size and supports approximate dp and dm values.
Practical Use Cases
Students can use this tool to check homework results quickly. Field teams can compare sites before deeper analysis. Teachers can explain how local magnetic vectors become global pole coordinates. Analysts can export the calculated values to spreadsheets or reports. The graph helps spot impossible results, longitude wrapping, and antipodal positions.
Good Practice
Use consistent longitude conventions across a project. Check whether east longitudes are positive. Record the polarity choice in notes. Do not combine uncorrected and corrected directions in one interpretation. Treat a single VGP as one observation, not a stable mean pole. For publication work, average multiple reliable directions, report uncertainty methods, and document every correction step.
Limits to Remember
The method assumes a geocentric dipole field. Real fields include secular variation, non dipole parts, and measurement noise. Therefore one pole can look scattered. More samples usually give a stronger mean. Check demagnetization quality, bedding correction, and age control. Then draw careful tectonic conclusions from the calculated pole in final reports for careful study.