Saint Lucia, and the rest of the Lesser Antilles islands were formed not only as a result of volcanic activity but also the subduction of underlying oceanic tectonic plates. Subduction can be defined as the slipping of one tectonic plate beneath another. In this area of the world, the underlying South American plate is ever so slowly slipping beneath the outer edge of the Caribbean plate resulting in the raising of the Caribbean plate; this interaction between these two plates causes both vulcanic activity (resulting in island formation) and earthquakes in the region.
Geothermal activity which is defined as the transfer of heat from depth to the earth's surface has its origins in volcanic activity. Water at depth can be heated through this process and manifests itself at the surface through three means: 1) hot springs, 2) fumaroles and 3) geysers.
Hot springs are the most common result of geothermal activity. Hot springs form when sufficient amounts of water seep through the earth's layers to a heat source below and then rises to the earth's surface through numerous channels forming quiet, bubbling pools.
When a hot spring does not have enough water to reach the earth's surface, the water is superheated underground into steam where it is released at the surface through vents also known as fumaroles. Where steam vents occur under surface water, chemicals in the steam can react to form sulphuric acid. The resulting sulphuric acid melts the underlying rock and creates warm, muddy pools also known as "mud pots".
Geysers are also formed as the result of water being heated underground and rising through the surface through channels in the underlying bedrock. Geysers, unlike hot springs and fumaroles, are lined with a material called geyserite which is dissolved out of the rock by the heated water. The geyserite is then deposited on the walls of the underground channels and hardens to such a degree that the channels become pressure tight. Near the top of the geyser's channels, the layering of geyserite constricts the opening near the surface; this constriction and the surface water act as a valve to keep pressure on deeper water which continues to heat more and more until it reaches its boiling point. At some point, the pressure below is too great for the constricted channel and surface water to contain and as the superheated deeper water is converted to steam it shoots out of the geyser. This allows more of the deeper water to continue to heat until it is converted into steam and the eruption continues until the pressure in the geyser's channel lessens.
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Logging Requirements:
To log this Earthcache, perform the following tasks and determine the answers to the questions below. Email me your answers, DO NOT include them with your Found It log.
- Is this site indicative of a hot spring, a fumarole or a geyser? Provide at least two reasons for your answer.
- What is the origin of the water at this site?
- What is the heat source for the water at this site?
- The water at this site has a distinctive colour; what colour is it and what has caused this to occur?
- There is a distinctive odour in the area. What does it remind you of? What is the primary mineral that is the cause of this odour?
