Minor Forms of
Extrusive Activity
Geysir
Stokkur, Iceland
Geysers are
hot springs that
erupt
periodically.
Water in the
lower crust is
heated by
rocks and turns
into steam;
pressure
increases and
the steam and
water explode
onto the
surface.
The
ingredients
needed for
geyser activity
are: heat,
water, and
underground
rock hard
enough to
withstand
intense
pressures.
Other features
A hot spring is a spring that is produced by the emergence of
geothermally heated groundwater from the Earth's crust.
There are hot springs all over the earth, on every continent
and even under the oceans and seas.
Boiling mud: hot water mixes with mud and surface deposits.
Lassen Volcanic Park
mudpot
A fumarole is an opening in Earth's crust, often in the
neighborhood of volcanoes, which emits steam and gases such
as carbon dioxide, sulfur dioxide, hydrochloric acid, and
hydrogen sulfide.
The name solfatara is given to fumaroles that emit sulfurous
gases.
Fumaroles may occur along tiny cracks or long fissures, in
chaotic clusters or fields, and on the surfaces of lava flows and
thick deposits of pyroclastic flows. A fumarole field is an area of
thermal springs and gas vents where magma or hot igneous
rocks at shallow depth are releasing gases or interacting with
groundwater. From the perspective of groundwater, fumaroles
could be described as a hot spring that boils off all its water
before the water reaches the surface.
Hverarönd sulphuric mud pools (solfataras). The ground is unstable there and you
cannot walk everywhere. Blue-gray mud is boiling and produces small or big
(depending on water content) bubbles that burst. The ground is yellow and reddish
and the noise from an abandoned hot water well is penetrating. The smell of sulphuric
dioxide is everywhere.
Close-up view of the solfatara at Ijen, Indonesia with
fumarole temperature of more than 220°C.