Upheavals in the Earth
Why does geyser throw out steam?
Geysers might be described as small distant cousins of volacanoes, for they too are created by the earth's internal heat.

Water from the surface penetrates deep down into long vertical cracks in the underlying rock which act as natural "water pipes." When this water sinks deep enough, the heat of the earth causes it to boil. Then the whole column of water and steam shoots up out of the top of the "pipe" to produce the beautiful fountain display for which geysers are famous. After the geyser has erupted, the whole process begins all over again.

Geysers exist in only three places in the world: Iceland, New Zealand and Yellowstone National Park in the western United States. Of these, the Yellow stone geysers are the most numerous and most spectacular. Yellowstone's most famous geyser, "Old Faithful," erupts at fairly regular intervals of about an hour.
Why does geyser throw out steam?