Indian geography 10

SEMI-VOLCANIC PHENOMENA

HOT SPRINGS

Overview

• Hot springs are springs that are produced by geothermally heated groundwater
  
  

  The Grand Prismatic Spring, a hot spring in the Yellowstone National Park (USA). The distinctive colour of the spring is due to thermophile - microorganims that thrive in high temperatures
• Hot springs range from tiny seeps to veritable rivers of hot water
• Hot springs are present all over the world, on all continents and even under the ocean
• The Dalhousie Springs in southern Australia are the largest hot springs in the world in terms of volume of water
• Water from hot springs has high mineral content, containing everything from calcium to lithium and even radium. For their high mineral content, hot spring are widely sought after spa destinations
• Thermophiles – organisms that thrive in temperatures 45-80 C – are found in hot springs and geysers

Sources of heat

• Hot springs are heated by geothermal heat
• Geothermal heat is the heat from the interior of the earth
• Geothermal heat can be produced by two natural phenomena: geothermal gradient and volcanic activity
• Geothermal gradient is the increase of temperature with depth inside the earth. Water that percolates deep inside the crust comes into contact with hot rocks and gets heated
• In areas of volcanic activity, water can also be heated by coming into contact with magma. The high temperature gradient near magma causes water to boil and even become superheated
• Hot springs in volcanic areas are almost always at or near the boiling point

List of important hot springs

Hot spring	Location	Notes
Aachen hot spring	Germany	The hottest springs in continental Europe (74 C)
Yangbaijing hot spring	Tibet	Several square km in size Probably the highest hot springs in the world Supplies a large part of the electricity for Lhasa
Icaria	Greece
Rio Hondo hot springs	Argentina	One of the most visited hot springs
Deildartunguhver	Iceland	Very high flow rate Very high water temperature (97 C) Used for heating neighbouring towns

GEYSERS

The Crystal Geyser in the Yellowstone National Park

• A geyser is a spring characterised by intermittent discharge of water ejected turbulently. The water discharge is accompanied by vapour (or steam) as well
• The word geyser comes from a spring in Haukadalur, Iceland called Geysir
• Geysers are temporary geological phenomena. The lifespan of geysers is a few thousand years at most.
• Generally all geyser sites are located close to active volcanic areas
• There are about a thousand known geysers in the world. Half of the world’s geysers are in the Yellowstone National Park, USA.
• Geysers are fragile phenomena and if conditions change, they can die. Many geysers have been destroyed by people throwing litter and debris into them, others have ceased due to dewatering by Geothermal power plants
• Geysers have been observed on the moons of other planets as well

Sources of activity

• Geysers are generally associated with volcanic areas, as the geyser effect is due to proximity of magma
• Surface water works its way down to a depth of about 2000 m, where it meets hot rocks of magma.
• The resultant boiling of the pressurised water results in the geyser effect of hot water and steam spraying out of the surface vent
• Geysers are relatively rare phenomena. They require a combination of three geological conditions
  • Intense heat: geysers need intense heat, which is provided by magma. The high pressures deep inside the earth raises the boiling point of water resulting in superheated water
  • Water: for geysers to exist, water must be available in the area. The water must be able to travel underground through deep pressurised fissures
  • Plumbing system: this includes a reservoir to hold the water while it is being heated and a vent on the surface for ejecting it. The plumbing system is made of a system of fissures, fractures, porous spaces that are essential for building up pressure before an eruption
    
    

    Distribution of major geysers in the world
• The geyser produces a material called geyserite that deposits onto the walls of the plumbing system making it pressure-tight. Geyserite is produced by rocks in the vicinity of the geyser, and consists mainly of silicon dioxide

Types of geysers

• Fountain geysers: erupt from pools of water in a series of intense violent bursts. Eg: Grand Geyser in Yellowstone National Park (USA)
• Cone geysers: erupt from cones or mounds of geyserite in steady jets that last from a few seconds to several minutes. Eg: Old Faithful Geyser in Yellowstone National Park (USA)

Important geysers in the world

Geyser	Location	Notes
Yellowstone National Park	Northwest USA	Home to half the world’s geysers World’s tallest predictable geyser: Grand geyser World’s tallest geyser: Steamboat geyser (300 ft) One of the most predictable geysers: Old Faithful
Valley of Geysers	Kamchatka Peninsula, Russia	Second largest concentration of geysers in the world Only geyser field in Eurasia
El Tatio	Chile	Very low height of eruptions (max 6 m)
Taupo Volcanic Zone	North Island, New Zealand	Was home to the world’s largest geyser: Waimangu Geyser (500 m) However, geothermal changes have changed the geyser field
Haukadalur Other places	Iceland	Geysers are distributed all over Iceland Famous geysers include Great Geysir and Stokkur

Cold water geysers

• Cold water geysers are similar to hot water geysers, except that carbon dioxide bubbles drive the eruption instead of steam
• In cold water geysers, carbon dioxide laden water lies in a confined aquifer trapped by less permeable overlying strata
• The column of water exerts enough pressure on the CO2 such that it remains in water in small bubbles
• When the pressure decreases due to formation of fissures, the CO2 bubbles expand and cause eruption
• CO2 laden water in cold water geysers are more white and frothy than hot water geysers
• Eg: Crystal Geyser in northwest USA, Geysir Andernach (Germany)
  
  

  A fumarole at the Halema Umau crater in Hawaii

Geysers in the solar system

• Geysers have been observed elsewhere in the solar system
• Unlike eruptions on earth, these geysers mainly consist of gas, dust and ice particles, without liquid
• Geysers have been observed on Saturn’s moon Enceladus, Neptune’s moon Triton and in the south pole of Mars

FUMAROLES

• A fumarole is an opening in the earth’s crust that emits steam and gases. Fumaroles occur in the neighbourhood of volcanoes
• Typical emitted gases include carbon dioxide, sulphur dioxide, hydrochloric acid and hydrogen sulphide
• Fumaroles occur when magma at shallow depths release gases or interact with groundwater releasing steam
• Fumaroles may persist for centuries if they occur over a persistent heat source, or disappear in weeks if they occur over fresh volcanic deposit that quickly cools off
  
  
  

  A mud pot in Namafjall, Iceland
• Eg: Valley of Ten Thousand Smokes (Alaska, USA), Yellowstone National Park (USA)

MUD POTS

• A mud pot is a hot spring or fumarole consisting of a pool of bubbling mud
• Mud pots form in high temperature geothermal areas where water is in short supply
• The little water that is available rises to the surface at a spot rich in volcanic ash, clay and other particles
• The mud takes the form of a viscous bubbling slurry
• Eg: Yellowstone National Park (USA)