Aguas Termales

Hot Springs

What are hydrothermal processes?

Strictly speaking, we refer to a set of processes that occur in the posthumous phases of volcanic activity, when much of the magma has already solidified or has come out as lava, and what is left is a set of residual liquids enriched in certain substances, but very different from the original magmas. Spoken in a broad sense, we refer to all phenomena involving water warmer than the surroundings.

What are the temperatures of the hot springs?

You will be surprised to know that the range of temperature variation is above 100 ° C. In fact, in order for the water to be considered as thermal, it must only meet the requirement of being at a temperature of 5 ° C or more above that of the soil in which it is found, or of the water flowing on the surface. This implies then that in very cold areas, the thermal water can also be of low temperature, as long as it obeys the aforementioned requirement.

For that reason the thermal waters can be classified according to their temperature as follows:

  • Cold thermal waters (less than 20ºC)
  • Hypothermal water (20-35ºC)
  • Mesothermal waters (35-45ºC)
  • Hyperthermal waters (45-100ºC)
  • Superthermal waters (100ºC and up)

Why is the temperature of the hot springs so variable?

Because it depends on its origin and the distance travelled from that location as well as other secondary factors (composition, temperature of the rocks that cross from its creation, geographical location, etc.)

What other classifications are there?

a) Mineralization

Based on the dry residue at 110ºC, the waters can be categorized into:


  • OLIGOMETALICS: dry residue at 110ºC lower than 100 mg/lt.
  • OF VERY WEAK MINERALISATION: when dry residue is found between 100 and 250 mg/lt.
  • WEAK MINERALISATION: when it is between 250 and 500 mg/lt.
  • MEDIUM MINERALISATION: when the residue is between 500 and 1000 mg/lt.
  • FROM STRONG MINERALISATION: the dry residue is above 1000 mg/lt.

b) The dominant anion / cation

When mineralization exceeds 1000 mg/lt, and an anion or cation exceeds 20% of total anions or cations, it is referred to as sulfate, chlorine, bicarbonate, sodium,calcium or magnesium waters.


If the mineralization does not exceed 1 gr/lt. only the predominant ion will be indicated, as in the previous case.


Sulphureted waters are those containing more than 1 mg/lt Sulfur, such as SH- or SH2

Carbonaceous waters are those containing more than 250 mg/lt of free CO2

Ferruginous waters are those containing more than 5 mg/lt iron

c) Radioactivity

Radioactive waters are considered to contain more than 67.3 Bq / lt of Radon gas.

e) Hardness

  • VERY SOFT WATERS: 0 to 100 mg / lt of CaCO3
  • SOFTWATER: 100 to 200 mg / lt of CaCO3
  • HARD WATER: 200 to 300 mg / lt of CaCO3
  • VERY HARD WATER: 300 to 400 mg / lt of CaCO3
  • EXTREMELY HARD WATER: more than 400 mg / lt of CaCO3

What is the origin of the hot springs?

It has been briefly mentioned already, but the two major causes are:

  • Hydro thermal process is related to volcanoes and igneous processes in general, which could be called hypogenic or deep-seated. Involves waters called juvenile or magmatic, due to their origin inside magmatic chambers where the rocks melted. Hypothermal and super thermal waters are generated in most cases. Good examples are solfataras and fumaroles.
  •  The epigene, which begins in the surface hydrological cycle, when the precipitation waters infiltrate and percolate until reaching abnormally high temperature sites (low geothermal gradient, a subject that should not frighten them because it is very simple but will be treated in detail in another post) where they are heated during circulation to the resurgence site. They usually give rise to cold, hypothermal and mesothermal hot springs at most. In general they are known as simple hot springs.

What is the composition of the hot springs?

It is also variable and depends both on its origin and on the crossed rock layers. So there are:

Ferruginous waters (mainly iron), chlorinated, sulfurized and sulphurous (with sulfur, which makes them quite hideous), sulfated (in which sulfur is combined in sodium, calcium, magnesium, etc. sulfates) or bicarbonated (where those elements mentioned in the previous parenthesis form bicarbonate)

What are the benefits of hot springs?

También es variable y depende tanto de su origen como de las capas rocosas atravesadas. Así pues, hay:

Aguas ferruginosas (que presentan fundamentalmente hierro), cloruradas (con cloro), sulfuradas y sulfurosas (con azufre, lo que las hace bastante hediondas), sulfatadas (en las que el azufre se combina en sulfatos de sodio, calcio, magnesio, etc.) o bicarbonatadas (donde esos elementos mencionados en el paréntesis anterior forman bicarbonato)

¿Cuáles son los beneficios de las aguas termales?

The mineralized hot water of the “spas” has different effects on the human body. Some authors divide them into three, biological, physical and chemical, although in reality all act at the same time.

Hot spring baths increase the temperature of the body, in addition it increases the hydrostatic pressure of the body, the reason why it increases the blood circulation and the oxygenation.

This increase in temperature helps to dissolve and remove toxins from the body.

By increasing oxygenation, the bath in hot springs improves the feeding of the tissues of the body in general, which is why it increases the metabolism, stimulating at the same time the secretions of the digestive tract and liver, thus helping digestion.

Repeated bathing (especially in periods of 3 to 4 weeks) may help normalize the functions of the endocrine glands as well as the overall functioning of the autonomous nervous system of the body.

There is also an improvement and stimulation of the immune system, mental relaxation and production of endorphins as well as regulation of glandular functions. Many of these effects are due to the body’s consumption of minerals such as carbon dioxide, sulfur, calcium and magnesium.

There are skin diseases that can have a marked improvement over baths in hot springs (especially if they contain sulfur). The diseases that are benefitted the most are psoriasis, dermatitis and fungal diseases.

Sometimes they also help in healing wounds and other skin lesions. Sometimes this action is attributed to “sulfobacteria” (an organism isolated by the “International Society of Hydrological Medicine” to explain the effects of the “intangible elements” of the hot springs.)

Not too many years ago, a microorganism was isolated, studying precisely what are called “intangible elements” of the hot springs. The isolated organism belongs to what is now called “sulfobacteria”. This group of microorganisms helps the human body to improve the skin defense system against all types of aggression.