Terrawatch: the South Atlantic Anomaly – a growing weak spot in Earth's magnetic field

Last year was a tumultuous one, but at least north is still north. Deep inside our planet liquid iron continues to flow the same way, generating a magnetic field that protects us against harmful radiation from the sun. Every so often the flow changes and the magnetic field flips. The last time this happened was 780,000 years ago. Could 2021 be the year when north becomes south?

One sign that the Earth might be gearing up for a magnetic reversal is a weakening of the field. We know that the Earth’s magnetic field has decayed by about 5% per century since measurements began in 1840. And much of that decay is associated with a strangely weak spot between South America and southern Africa, known as the South Atlantic Anomaly. This patch has grown over the last 250 years and today the weak field messes with satellite technology.

So how new is this anomaly? After analysing volcanic rocks from the southern Atlantic island of Saint Helena geologists from the University of Liverpool have shown that the magnetic field has been playing up here for millions of years, suggesting the South Atlantic Anomaly is a long-term fixture, and not a sign that the Earth’s magnetic field is about to flip.