Mafic
An igneous composed chiefly of one or more dark-coloured minerals.
Magma
Magma is a mixture of molten rock, crystals and gases present beneath the Earth’s surface. It usually accumulates in magma chambers before erupting at the surface. Magma is divided into
types according to silica (SiO2) content, which controls viscosity (ease of flowing) and hence influences eruptive styles. The most silica-poor (45–55 wt.% SiO2) fluid magmas are called basaltic magmas. Andesitic and dacitic magmas have intermediate compositions (55–63 wt.% and 63–70% SiO2, respectively). Themost silica-rich, viscous magmas (> 70 wt.% SiO2) are called rhyolitic magmas.
Magma Chamber
The subterranean cavity containing the gas-rich liquid magma which feeds a volcano.
Magmatic
Pertaining to magma.
Magmatic eruptions
Explosive magmatic eruptions occur when dissolved gases in a rising magma expand to form gas bubbles which then burst as the magma nears the Earth’s surface, leading to explosive fragmentation of the magma.
Magnitude
The magnitude is a number that characterizes the relative size of an earthquake. Magnitude is based on measurement of the maximum motion recorded by a seismograph. Several scales have been defined, but the most commonly used is the local magnitude (ML), commonly referred to as “Richter magnitude”. All magnitude scales should yield approximately the same value for any given earthquake.
Main shock
Is the largest earthquake in a series/sequence, sometimes predicted by one or more foreshocks and almost always followed by many aftershocks.
Mantle
The part of the earth’s interior between the metallic outer core and the crust.
Microzonation
The identification of separate individual areas having different potentials for hazardous earthquake effects.
Modified Mercalli Intensity (MMI)
The MMI is a value assigned to a specific site or location after an earthquake, which gives an indication of the observed level of intensity and which is based on a scale that ranges from imperceptible shaking to catastrophic destruction
Moho
The Moho is the boundary between the crust and the mantle in the earth. This is a depth where seismic wave changes velocity and there is also a change in chemical composition. Also termed the Mohorovicic discontinuity. The boundary is between 25 and 60 km deep beneath the continents and between 5 and 8 km deep beneath the ocean floor.
