Volcano information and links to websites
Video documentary by the National Geographic “Down to the Earth’s Core” – a dramatic and quite visually stunning journey into the centre of the earth.
A good use of drones to capture volcano close-up:
International Volcanic Health Hazard Network http://www.ivhhn.org/ A very useful site for this topic
All aspects of volcano hazards are dealt with on the USGS Volcano Hazard pages.
A pyroclastic flow will destroy nearly everything in its path. With rock fragments ranging in size from ash to boulders traveling across the ground at speeds typically greater than 80 km per hour, pyroclastic flows knock down, shatter, bury or carry away nearly all objects and structures in their way. The extreme temperatures of rocks and gas inside pyroclastic flows, generally between 200°C and 700°C, can cause combustible material to burn, especially petroleum products, wood, vegetation, and houses.
Pyroclastic flows vary considerably in size and speed, but even relatively small flows that move less than 5 km from a volcano can destroy buildings, forests, and farmland. And on the margins of pyroclastic flows, death and serious injury to people and animals may result from burns and inhalation of hot ash and gases.
Pyroclastic flows generally follow valleys or other low-lying areas and, depending on the volume of rock debris carried by the flow, they can deposit layers of loose rock fragments to depths ranging from less than one meter to more than 200 m. Such loose layers of ash and volcanic rock debris in valleys and on hillslopes can lead to lahars indirectly by:
1. Damming or blocking tributary streams, which may cause water to form a lake behind the blockage, overtop and erode the blockage, and mix with the rock fragments as it rushes downstream (for example, see this case study at Pinatubo Volcano, Philippines)
2. Increasing the rate of stream runoff and erosion during subsequent rainstorms. Hot pyroclastic flows and surges can also directly generate lahars by eroding and mixing with snow and ice on a volcano’s flanks, thereby sending a sudden torrent of water surging down adjacent valleys (see case study from Nevado del Ruiz volcano, Colombia).
A’a and pahoehoe flow in Hawaii
Pahoehoe is a Hawaiian term for basaltic lava that has a smooth, hummocky, or ropy surface. A pahoehoe flow typically advances as a series of small lobes and toes that continually break out from a cooled crust. The surface texture of pahoehoe flows varies widely, displaying all kinds of bizarre shapes often referred to as lava sculpture. Follow the link to pictures of this kind of flow.
Both Pahoehoe and Aa lavas are basaltic in composition and therefore have effectively the same silica content. It seems that the difference relates to the amount of air or other gases within the lava rather than a difference in mineral chemistry.
The theory of mass extinction of the dinosaurs due to volcanic eruptions is perhaps out-dated, as new hypotheses suggest more likely explanations, but the following video is good from the point of view of volcanic effects on the atmosphere: https://www.youtube.com/watch?v=uTvFzm3jRCU