GeologyRocks

Lahar

A mudflow associated with volcanic eruptions when volcanic ash mixes with water.

Limestone

A rock composed mainly of calcium carbonate CaCO₃. Limestones comprise a large variety of rocks including carbonate muds and oozes, chalks, ooliths and bioclastic limestone. They form in a variety of environments from deep sea (but above the carbonate compensation depth), temperate seas, tropical sea, lakes and rivers. Most caves are found in limestones due to erosion by acidic water. Limestones erode into karst topography.

Limestone Pavement

A formation found in areas of karstic topography where limestone has dissolved into pavement-like blocks. The dissolution occurs along joints forming grykes. This leaves blocks called clints.

Picture courtesy of Benauld.

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.

Lithosphere

The outer, rigid shell of the earth. It is composed of the entire crust and uppermost part of the mantle. The thickness of the lithosphere varies from around 5km to up to 100km where there is thick continental crust. The lithosphere is above the more ductile asthenosphere. The boundary between these two layer is the Mohorovicic discontinuity.

The lithosphere is fragmented into tectonic plates which move relative to one another. This movement of lithospheric plates is described as plate tectonics.

Lustre

The way in which a mineral shines in light and described using terms such as vitreous, adamantine, etc. However, there are no rigid boundaries between the different terms.