Haukadalur is a geologically active valley that is a stopping point on what is called the Golden Circle tour. The main reason for many folk calling here can be seen in the photo: the Strokkur geyser. This gusher erupts fairly frequently so that is why it gets surrounded by folk awaiting them. It was an earthquake that set it going in the eighteenth century when the conduit was opened and that was closed around the beginning of the twentieth century by another earthquake. That was how things were until the 1960's when locals cleared the conduit on the advice of the Geysir committee to set in train the sights that have drawn so many since then.
Strokkur, or churn in Icelandic, is not alone for there is Geysir and little Geysir. The first of these once was the main attraction but it has taken earthquakes to set it off in recent times. Even so, the name Geysir is the origin of the more general term geyser and itself is the Icelandic for gusher. You also need to be careful where you step around these since there also is a geothermal spring called Konungshver that rises and flows hereabouts so you may scald yourself simply by stepping into any flowing water. The air is full of a sulphurous stench too so reminders of geological activity are everywhere in this spot.