Geysir eruption

From Summer 2010

In the linked album there are 3 other pictures, showing the Strokkur geysir before and during eruption. There you will also find pictures from Thingvellir, and birds and flowers that I took this summer.

Geysir activity – how/why geysir erupts

Geyser activity, like all hot spring activity, is caused by surface water gradually seeping down through the ground until it meets rock heated by magma.

The geothermally heated water then rises back toward the surface by convection through porous and fractured rock.

Geysers differ from non-eruptive hot springs in their subterranean structure; many consist of a small vent at the surface connected to one, or more, narrow tubes that lead to underground reservoirs of water.
As the geyser fills, the water at the top of the column cools off, but because of the narrowness of the channel, convective cooling of the water in the reservoir is
impossible.

The cooler water above presses down on the hotter water beneath, not unlike the lid of a pressure cooker, allowing the water in the reservoir to become superheated, that is, to remain liquid at temperatures well above the boiling point.

Ultimately, the temperatures near the bottom of the geyser rise to a point where boiling begins; steam bubbles rise to the top of the column. As they burst through the geyser’s vent, see Figure in album, some water overflows or splashes out, reducing the weight of the column and thus the pressure on the water underneath. With this release of pressure, the superheated water flashes into steam, boiling violently
throughout the column, see Figure above and in album.

The resulting froth of expanding steam and hot water then sprays out of the geyser.

Eventually the water remaining in the geyser cools back to below the boiling point and the eruption ends; heated groundwater begins seeping back into the reservoir, and the whole cycle begins again.

The duration of eruptions and time between successive eruptions vary greatly from geyser to geyser; Strokkur in Iceland erupts for a few seconds every few minutes, while Grand Geyser in the USA erupts for up to 10 minutes every 8-12 hours.