This Earth Cache is located just off the shore in relatively shallow waters, but you will need a snorkel or scuba equipment to locate the thermal vents. [2022 edit] I have increased the difficulty and added 'rocks' and 'thorns' to the attributes list due to the overgrown pathway. You may want to take beach shoes or something sturdy to walk in / wear.
Recommended parking is alongside the road and then walk down the path, as the rocks can easily puncture a tyre or cause damage with plenty of potholes around. An overgrown footpath leads you the the top of a coral and stone embankment with a rudimentary 'staircase' of sorts. The vents are located almost immediately straight out from the way down. At the base of the path there is a large driftwood tree trunk just to the right. The trunk makes for an ideal spot to drop your gear and prepare for your water entry.
The water depth of the general area is 4-6 feet and there is not usually any strong wave action or currents. Head about 10-15 feet out into the water and you will see the yellowish plumes of gas and fresh water mix with the seawater, creating a blurring effect known as Halocline.
Earth Lesson:
Surprisingly, hydrothermal vents were only discovered in 1977 (the much-celebrated year of Geo_Bro's birth!) and are typically found underwater on the boundaries of tectonic plates. Geo_Bro also remembers a university project concerning bacterial microbes living in the extremely high temperatures of thermal vents. Distributed around the world, there are over 500 thermal vent sites, but few are in the Caribbean, making this EarthCache site particularly noteworthy.
Sea water is drawn into the hydrothermal system through faults and porous sediments or volcanic strata, plus some magmatic water released by the upwelling magma from the earth's core. Ambient water temperature of the deep sea can be 0-3 °C, which is heated upon contact with the magma. Water emerges from these vents at temperatures ranging from 60 °C (140 °F) up to as high as 464 °C (867 °F). Due to the high hydrostatic pressure at these depths, water may exist in either its liquid form or as a supercritical fluid at such temperatures. The critical point of (pure) water is 375 °C (707 °F) at a pressure of 218 atmospheres. However, introducing salinity into the fluid raises the critical point to higher temperatures and pressures. The critical point of seawater (3.2 wt. % NaCl) is 407 °C (765 °F) and 298.5 bars, corresponding to a depth of ~2,960 m (9,710 ft) below sea level. Accordingly, if a hydrothermal fluid with a salinity of 3.2 wt. % NaCl vents above 407 °C (765 °F) and 298.5 bars, it is supercritical. Furthermore, the salinity of vent fluids have been shown to vary widely due to phase separation in the crust. The critical point for lower salinity fluids is at lower temperature and pressure conditions than that for seawater, but higher than that for pure water. For example, a vent fluid with a 2.24 wt. % NaCl salinity has the critical point at 400 °C (752 °F) and 280.5 bars. Thus, water emerging from the hottest parts of some hydrothermal vents can be a supercritical fluid, possessing physical properties between those of a gas and those of a liquid.
Some hydrothermal vents form roughly cylindrical chimney structures called a precipitation chimney or stack. These form from minerals that are dissolved in the vent fluid. When the superheated water contacts the near-freezing sea water, the minerals precipitate out to form particles which add to the height of the stacks. Some of these chimney structures can reach heights of 60 m. An example of such a towering vent was "Godzilla", a structure on the Pacific Ocean deep seafloor near Oregon that rose to 40 m before it fell over in 1996.
A black smoker or deep sea vent is a type of hydrothermal vent found on the seabed, typically in the bathyal zone (with largest frequency in depths from 2500 m to 3000 m), but also in lesser depths as well as deeper in abyssal zone. They appear as black, chimney-like structures that emit a cloud of black material. Black smokers typically emit particles with high levels of sulfur-bearing minerals, or sulfides. Black smokers are formed in fields hundreds of meters wide when superheated water from below Earth's crust comes through the ocean floor (water may attain temperatures above 400 °C). This water is rich in dissolved minerals from the crust, most notably sulfides. When it comes in contact with cold ocean water, many minerals precipitate, forming a black, chimney-like structure around each vent. The deposited metal sulfides can become massive sulfide ore deposits in time. The world's deepest known black smokers are located in the Cayman Trough, 5,000 m (3.1 miles) below the ocean's surface.
White smoker vents emit lighter-hued minerals, such as those containing barium, calcium and silicon. These vents also tend to have lower-temperature plumes probably because they are generally distant from their heat source. Black and white smokers may coexist in the same hydrothermal field, but they generally represent proximal and distal vents to the main upflow zone, respectively. However, white smokers correspond mostly to waning stages of such hydrothermal fields, as magmatic heat sources become progressively more distant from the source (due to magma crystallization) and hydrothermal fluids become dominated by seawater instead of magmatic water. Mineralizing fluids from this type of vents are rich in calcium and they form dominantly sulfate-rich (i.e., barite and anhydrite) and carbonate deposits.
Requirements:
The log this EarthCache, please send me an email or message containing the answers to the following questions:
- What is the temperature of the sea, approximately, in the shallow waters upon entry? A rough estimate based upon your body temperature and apparent 'feel' on entry, or some internet research will suffice.
- What, if anything, can you smell at the water entry point? If the wind is blowing then please hazard a guess as to what you may be able to smell, where it has come from and what chemical compound might this be?
- How does a geothermal vent stack form? What was the name, height and location of the largest recorded stack?
- Describe what stack formations, if any, can you see at the EarthCache site? What does this tell you about these vents?
Please feel free to log a photo, if you can, of any geothermal activity you can see. Or, alternatively, record some of the beautiful scenery of the North Side whilst you are here.