[I thought I would try something different. Let me know if you think it works. Indeed, let me know of any comment you may have. I keep saying this, but the Substack app (on phone, tablet, laptop) is the best way to view, and respond to, posts.
Finally, can I recommend three other Substacks, which I consider to be very useful to A level students – those of Will Fry (Changing places), Hannah Ritchie (Sustainability by Numbers) – her latest post on Climate change and death rates is brilliant (posted Oct 14th) - and Ann Pettifor (System change). All are free.]
Questions
a. On average, how many volcanoes erupt each year worldwide?
b. Which type of magma generally causes violent, explosive eruptions?
c. When was the last time more than 500 people were killed by a single volcanic eruption?
d. What was first discovered on the ocean floor in the 1960s, providing key evidence for plate tectonics?
e. Which one of these earthquakes is the odd one out and why? Banda Aceh, Indonesia (2004); Tohoku, Japan (2011); Talcahuano, Chile (2010); Port-au-Prince, Haiti (2010).
f. What secondary hazard do the following earthquakes have in common: Kashmir (2005); Sichuan, China (2008); Nepal (2015)?
g. Using the map below, match the names of the five famous volcanoes (eruption dates in brackets) to the letters A–E.
Mt Vesuvius (AD 79)
Mt Pinatubo (1991)
Yellowstone caldera (640,000 BP)
Soufriere Hills (1995)
Eyjafjallajökull (2010)
h. Which volcanic hazard has been responsible for most deaths in the last 124 years?
i. What impact, albeit only for a few years each, have large volcanic eruptions had on the Earth’s climate?
Mount Ontake (2014)
Answers
a. On average, about 50-70 volcanoes erupt every year. Some of them erupt multiple times, while others only have one eruption. The typical number of individual eruptions per year is therefore more in the range of about 60-80.
b. Andesitic. Andesite is an igneous rock with a high dissolved gas content, high silica content and low eruption temperature (compared to basalt). It is viscous as a magma and hence erupts explosively.
c. The last time was 1991 when Mt Pinatubo erupted in the Philippines, killing around 850 people. Subsequent eruptions have had a lower death toll, for example Nyiragongo in 2002 (250), Merapi in 2010 (350) and Ontake in Japan in 2014 (57) (photo). Deaths from volcanic eruptions are relatively rare in comparison to earthquakes.
d. Magnetic stripes. These ocean-floor features essentially proved that new oceanic plate was created at constructive plate margins - a theory first put forward by Harry Hess and demonstrated by Vine and Mathews.
e. Haiti in 2010. The other three occurred at subduction zones whereas Haiti happened on a conservative margin (transform fault). The others all generated significant tsunami whereas Haiti did not.
f. Landslides. All three earthquakes occurred in the Himalaya which is a belt of geologically young and unstable mountains with steep-sided valleys cut by rivers.
g. A - Yellowstone; B - Soufriere Hills; C – Eyjafjallajökull; D – Vesuvius; E - Pinatubo
h. Pyroclastic flows. For example, most of the 30,000 killed by the eruption of Mt Pelée on Martinique in 1902 were killed by pyroclastic flows.
i. Global cooling. The eruption of Mt Pinatubo in 1991 is estimated to have caused global cooling of about 0.5°C; the eruption of Tambora in 1815 may have cooled the planet by up to 0.7°C.
