NH
Natural Hazards

Archives / 2018 / October

Volcanic eruptions: Sometimes natural spectacles, but other times disasters

In April 2018, an eruption of the Kilauea volcano in Hawaii started. The activity continued for months, with impressive lava flows that cut roads and even covered houses and entire neighbourhoods (Figure 1), forcing the evacuation of thousands of people. Fortunately, it did not take any life. Some weeks later, on June 3rd,  Fuego volcano, in Guatemala, shocked the international community with a shorter, but certainly more violent, eruption. The eruption of Fuego volcano, probably less known than Kilauea, affected near two millions of people and sadly caused 190 verified deaths and 238 missing persons.

 

Figure 1. Comparison of satellite images before (left) and after (right) the Kilauea eruption at Leilani Estates subdivision, Hawaii. The area was covered by lava flows. Image credit: USGS.

The main reason why Fuego’s eruption was more deadly than the Kilauea’s one is the type of activity. They are different types of volcanoes with different eruptive dynamics and thus different related hazards. Kilauea is a shield volcano and it is formed by a sequence of eruptions of very low viscous magma. The magma reaches the surface and is generally erupted in an effusive way generating lava flows, really hot mixtures of molten rock, crystals and gas emitted from the volcanic vent, able to reach several meters per second  and kilometers of length, literally looking like rivers (such as in this video). These lava flows can be sometimes accompanied by weak to mild explosive activity in the form of lava fountains. [Read More]

Earthquake-induced landslides and the ‘strange’ case of the Hokkaido earthquake

The population of many countries in the world is exposed to earthquakes, one of the most destructive natural hazards. Sometimes, consequent triggered  phenomena can be even worse than the earthquake itself. In this context, earthquake-induced landslides often concur in life and economic losses. To better understand these induced phenomena, updated catalogues of their types and location of occurrence are fundamental. In his works, Dr David K. Keefer performed several interesting statistical analysis, which highlighted how the magnitude and the distance from the epicentre play a key role in triggering earthquake-induced landslides (Figs. 1 and 2). In particular, he showed that the number of landslides induced by earthquakes decreases with the increase in distance from the epicentre (Fig.1) and that the number of landslide increases with larger magnitude events (Fig. 2). [Read More]