The Nature of Volcanic Eruptions
- Volcanic activity is commonly perceived as a process that produces a picturesque, cone-shaped structure that periodically erupts in a violent manner.
- To varying degrees, these factors affect the magma's mobility, or viscosity.
- The amount of volatiles contained in magma also affects its mobility. Other factors being equal, water dissolved in the magma tends to increase fluidity because iit reduces polymerization by breaking silicon-oxygen bonds.
- One of the simplest mechanisms for triggering a volcanic eruption is the arrival of a new batch of melt into a near surface magma reservoir.
- All magmas contain a small percentage of water and other valtiles that are held in solution by the immense pressure of the overlaying rock.
- The vast majority of lava on Earth, more than 90% of the total volume, is estimated to be basaltic in composition.
- Two types of lava flows are known by their Hawaiian names. The most common of these aa flows, have surfaces of rough jagged blocks with dangerously sharp edges and spiny projections.
- Hardened basaltic flows commonly contain tunnels that once were nearly horizontal conduits carrying lava from the volcanic vent to the flow's leading edge.
- Lava tubes are important because they allow fluid lavas to advance great distances from their source.
- In contrast to fluid basaltic magmas which typically produce pahoehoe and aa flows, andesitic and rhyolitic magmas tend to generate block lavas.
- Pillow lavas are useful in the reconstruction of Earth history because whenever they are observed, they indicate that the lava flow formed in an underwater environment.