When Indonesia's Anak Krakatau volcano began erupting on September 4, thousands of flights were grounded. Hundreds of thousands of passengers were stranded. Volcanic ash is dangerous for aircraft because it can damage engines or even make them stall. It can also scratch cockpit windows, which reduces what pilots can see. Toxic gases such as sulphur dioxide may contaminate cabin air.
A European satellite called EarthCARE gave experts useful data. It was designed mainly to study how clouds and tiny airborne particles affect the climate. One of its four instruments, a laser called ATLID, sends pulses of ultraviolet light toward Earth. By measuring the light that scatters back, it shows how high the particles are and how concentrated. Combined with advanced algorithms, it can even help estimate particle types such as ash, smoke, or dust. The volcanic ash centre in Darwin, Australia, quickly added this data to its monitoring tools. The data also help scientists learn how eruptions change the climate.