A new study finds the magnetic field generated by a tsunami can be detected a few minutes earlier than changes in sea level and could improve warnings of these giant waves.

Tsunamis generate magnetic fields as they move conductive seawater through the Earth’s magnetic field. Researchers previously predicted that the tsunami’s magnetic field would arrive before a change in sea level, but they lacked simultaneous measurements of magnetics and sea level that are necessary to demonstrate the phenomenon.

The new study provides real-world evidence for using tsunamis’ magnetic fields to predict the height of tsunami waves using data from two real events—a 2009 tsunami in Samoa and a 2010 tsunami in Chile—that have both sets of necessary data. The new study was published in AGU’s Journal of Geophysical Research: Solid Earth, which focuses on the physics and chemistry of the solid Earth.