You may have noticed already that there are white colored rings and mounds around the edges of the fumaroles, hot springs and geysersthat look like salt or snow. Some geysers, like Beehive Geyser and Castle Geyser, even have large white cones built up around the vents releasing the water (shown in the picture of Castle Geyser below). These white rings and cones are not salt nor snow; they are mineral deposits called sinter.
Sinter comes from silica that has been heated up by the water in the earth’s crust. The hot water contains silica from the underlying rhyolite bedrock. When the water reaches the earth’s surface, it cools and the minerals condense to form deposits and accumulate along the edges of the fumaroles, hot springs, and geysers.
It is the white color of the sinter deposits that inspired the naming of Porcelain Basin. As the hot springs and geysers shed their water across the basin, the minerals are deposited and cover the ground like a sheet. The sinter usually accumulates very slowly, less than one inch per century. Over time they build up to form the geyser cones and mounds seen in most geyser basins. It is interesting that if the mineral deposits seal off a hot spring or geyser by accumulating in its vent, the hot, pressurized water may flow underground to another weak area and blow through it, creating a new geyser.
