Type of EarthCache: Hydrologic Feature
Formation of hot springs
Most precipitation in the form of the rain and snow that falls on the slopes of a mountain ends up in rivers and streams. Some of it, however, percolate down through the soil or pores and fractures in rocks forming groundwater. After traveling for some distances, if this groundwater resurfaces and is discharged at a specific location it is called a spring.
However, if this meteoric water percolates deep enough into the ground they would be heated up by the Earth’s interior heat. In general, the temperature of rocks within the Earth increases with depth. The rate of temperature increase with depth is known as the geothermal gradient. The geothermal gradient is the rate at which the Earth's temperature increases with depth, indicating heat flowing from the Earth's hot interior to its cooler surface. Away from tectonically active region, it is 25-30°C per km of depth in most part of the world.
In volcanic regions, the high temperature gradient cause water to be heated hot enough that it boils or becomes superheated. If the water becomes so hot that it builds steam pressure and erupts in a jet above the surface of the Earth, it’s called a geyser. If the water only reaches the surface in the form of steam, it’s called a fumarole. And if the water is mixed with mud and clay, it’s called a mudpot.
In tectonically inactive parts of the world, water that percolates down by gravity through permeable or fractured rocks would be heated gradually. At depths of 3 km or more the rock temperature is at or above the boiling point of water at the surface of the Earth. At these great depths, the pressure is too high for water to boil. However, hot water is less dense than cold water, and expanding gases in it also decrease its overall density. If given the chance, the hot water will rise over cold water and reached the surface in the form of hot springs, which have a water temperature that is above the average ambient. This could be anywhere from near air temperature up to the boiling point (100°C) of water. The water from hot springs in non-volcanic areas is heated in this manner (Figure 1).
Figure 1: Formation of hot spring in tectonically inactive region (MaliBooBoo, 2009).
The rise of this hot water to the surface is facilitated by the presence of fractured rocks or fault planes that provide upward conduits to the surface. As this water rises, replacement cold water is drawn in from the surrounding rocks, keeping a continuous circulation of water in the hot spring system. Hot springs range in flow rates from the tiniest "seeps" to veritable rivers of hot water.
Degree of hotness of a hot spring
How hot the water of a hot spring depends on a number of factors;
1. The geothermal gradient of the region.
2. The depth the groundwater reached.
3. The rate the hot water surfaces. Normally the hot water at depth cannot force its way up through the rocks fast enough to retain the heat, which is lost as it moves up into cooler layers, so it stops rising before it reaches the surface. If it reaches the surface quickly enough, it will be very hot. If it takes a long time to reach the surface, the water will be sufficiently cooled before reaching the surface.
4. The degree the hot water mixes with normal groundwater near the surface, causes the resulting hot springs to have different temperatures.
Hydrogen sulphide odour
As the water heats up, it dissolves minerals in the surrounding rock. Many hot springs have a sulphur smell which is caused by anaerobic bacteria living deep beneath the Earth’s crust. The anaerobic bacteria convert the sulphur bearing minerals in the rocks into hydrogen sulfide, imparting a “rotten eggs” odour. If the hot spring does not have a sulphurous odour it may be due to a couple of reasons (Dark Energy, 2011):
1. There is no sufficient amount of sulphur bearing minerals in the rocks. The most common sulphur bearing minerals are pyrite and gypsum.
2. The groundwater does not reach sufficient depths for conversion of sufficient sulphur bearing minerals to hydrogen sulphide.
3. The hot water that return to the surface is oxidized and losses its hydrogen sulphide.
Surface encrustation
As the hot spring water bubbles from its underground source to the surface, it begins to precipitate out the minerals it gained on its travels through the rocks. The types of encrustations around a hot spring depend on the rock type in the hot spring region. The encrustation could be travertine, siliceous sinters or sulfur.
Travertine is a terrestrial sedimentary rock, formed by the precipitation of calcium carbonate from solution in surface or ground waters, or geothermally heated hot-springs. Typically rocks that produce travertine are rich in calcium carbonate, e.g. limestone and marble. Travertine exists in white, tan and cream-colored varieties.
Encrusted siliceous sinters are typically white solids occurring as deposits around geysers or hot springs. Typically rocks that produce siliceous sinters are rich in silica, e.g. granite and quartzite. Red, brown, yellow varieties siliceous sinters are also found depend on different mineral mixtures (primarily hydrous oxides of iron).
Sulfur occurring as bright yellow solid can be found near hot springs as a result of reduction of sulphur bearing minerals from the rock through which the hot water flow.
Microclimate around hot spring
Anaerobic bacteria in hot springs also break down available minerals and when exposed to the surface, provide excellent fertilizers for algae and other plant life. The microclimate around a hot spring attracts an abundance of algae and bacteria to live in it. Drinking hot spring water is discouraged due to these reasons unless it is regularly tested for consumption. Drinking from the hot spring should be avoided.
Hot Spring: Sungai Berok, Kelantan
Sungai Berok hot spring is situated in the state of Kelantan. It is located directly on top of the Main Range granitic plutons that form the backbone of the mountain ranges of Peninsular Malaysia (Figure 2). This region, as elsewhere in Peninsular Malaysia, is tectonically inactive. The main rock types of these granitic plutons are coarse to very coarse grained megacrystic biotite granites (Azman, 2009). The ages of these plutons are 207-230 Ma, i.e. Upper Triassic (Bignell & Snelling, 1977; Liew, 1983; Darbyshire, 1988).
Figure 2: Location of Sungai Berok hot spring (modified after Azman, 2009).
How to claim this EarthCache?
Field equipment required: A calibrated thermometer that measures temperatures from 0 to 100°C.
Send me the following;
1. The text "GC7CJG7 Sungai Berok - Hot Spring" on the first line.
2. The answers to the following questions;
- Measure the temperature of the hot spring at its source (at the listed coordinates).
Use the following standard protocol for measuring temperature (andrewgwalters, 2010);
i. Hold the thermometer by the end or by attached string.
ii. Place the end of the thermometer that has the bulb into the water so that the bulb is fully submerged.
iii. Leave the thermometer submerged in the water for 60 seconds. This will allow the thermometer to fully adjust to the new temperature. Especially when the water is hot, it will take some time for the thermometer to change and reflect the correct temperature.
iv. While the thermometer is still in the water, locate the red line on the thermometer, and find the highest point where it crosses the numbered black lines.
v. Record the temperature to the nearest degree.
- Note what you smell and see at the source of the hot spring;
(i) How strong is the smell of hydrogen sulphide? Very strong, strong, slight, or very slight? Why?
(ii) How much of the surrounding granitic rocks were encrusted by minerals deposited by the hot spring? 100%, 75%, 50%, 25%, or 0%.
(iii) What is the colour of the encrustation? Why do you think it is of that colour?
(iv) Do you see algae growth in the water or on the surrounding granitic rocks? What are their colours? Why do they seem to be striving there?
- The temperature you've recorded. At this temperature, given that the EarthCache site is in a tectonically inactive region, estimate at what depth the hot water rises from? Assume there is no change in temperature of the hot water at depth and at the surface and the geothermal gradient follows a linear function. This question is just to get an idea how deep the hot spring reservoir is if the temperature of the reservoir is similar to the temperature of the hot water at the surface.
3. Provide a photo of yourself or a personal item to prove you have visited the site.*
References
1 Andrew G. Walters, 2010. GC2FW3X: Ohanapecosh - Hot Springs By Gosh! Washington, USA Groundspeak Inc., Seattle, Washington, USA [online]. Available from http://coord.info/GC2FW3X [accessed on 6 Aug 2012]. 2 Azman, A.G., 2009. Plutonism. In: Hutchison, C.S. and Tan, D.N.K. (eds.), 2009. University of Malaya and Geological Society of Malaysia, Kuala Lumpur, 211-232. 3 Bignell, J.D. and Snelling, N.J., 1977. Geochronology of Malayan granites. Overseas Geology and Mineral Resources, 47, Institute of Geological Sciences, H.M. Stationery Office, London, 72 pp. 4 Darbyshire, D.P.F., 1988. Geochronology of Malaysian Granites. NERC Isotope Geological Report, British Geological Survey, 3, 60 pp. 5 Dark Energy, 2011. GC2P566: Hot Spring: Kampung Ulu Slim, Perak. Malaysia. Groundspeak Inc., Seattle, Washington, USA [online]. Available from http://coord.info/GC2P566 [accessed on 5 August 2012]. 6 Liew, T.C., 1983. Petrogenesis of Peninsular Malaysia granitoid batholiths. Unpubl. Ph.D. thesis, Australian National University. 7 MaliBooBoo, 2009. GC1W8JC: Sloquet Hot Springs Earthcache. British Columbia, Canada. Groundspeak Inc., Seattle, Washington, USA [online]. Available from http://coord.info/GC1W8JC [accessed on 6 Aug 2012].
* Effective immediately from 10 June 2019, photo requirements are permitted on EarthCaches. This task is not optional, it is an addition to existing logging tasks! Logs that do not meet all requirements posed will no longer be accepted.
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Finding the answers to an EarthCache can often be challenging, and many people tend to shy away from these caches because of this. However, it is my opinion that geocaching is also meant to be a fun family experience that simply aims to introduce interesting and unique locations such as this one. Flexibility on logging requirements, however, can only be applied if it can be established that you have actually taken the time to visit the site. For this reason, a proper log describing your adventure accompanied by a good number of photos would be much appreciated.
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