Eldgjá, also known as "fire canyon," is a volcano and canyon located in Iceland. It's part of the Katla volcano and stretches for about 40 kilometers. Back in 939 CE, Eldgjá experienced a massive eruption, which was actually the largest effusive eruption in recent history. This eruption covered a whopping 780 square kilometers of land with lava. The impact of this eruption was felt far beyond Iceland, causing a noticeable cooling of the climate and leading to cold winters and food shortages across Eurasia. So yeah, it was a pretty big deal!