How would you define the following terms: frost wedging, lithification, metamorphosis and unloading?

• Frost Wedging - also known as congelifraction, frost weathering or frost shattering.
  When a rock is exposed such that water is liquid during the day, but freezes at night, the expansion of the freezing water can cause stress in the rock such that it can shatter. This is most common in deserts where water in the rock will freeze rapidly during the night.
• Lithification -
  The process of turning loose sediment into a sedimentary rock. This is done by heat, pressure and time. This process can take from years to millions of years. Hardgrounds are formed in inter-tidal carbonates and can form in years. Usually this process is a slow one. If this process continues, metamorphism occurs.
• Metamorphosis -
  Metamorphosis require heat, pressure and time and is an extension of lithification, but it can occur on any rocks type (including metamorphic rocks). There is a continuum of type from heat dominated (marble) to pressure dominated (blueschist). Metamorphism is ranked in terms of a grade. A high grade metamorphic rock is a gneiss, which has undergone intense heat and pressure. It is important to note metamorphism occurs in the solid state - there is no melting. If the rock starts to melt it is called a migmatite (Mixed IGneous and metamorphic rock).
• Unloading -
  Unloading is simply the removal of overburden by erosion or tectonic movement. This causes the release of stress which usually results in pressure release formations. A good example is the tilting of the UK due to the removal of ice sheets in the north. Scotland is moving upwards, southern Britain is moving downwards. The evidence can be seen in raised beaches in Scotland, which gives the past sea level.

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