Earthquakes, Volcanoes and the Restless Earth – answers and explanations
Here are the answers to all 15 questions in the Earthquakes, Volcanoes and the Restless Earth quiz, each with a short explanation. Quakes, eruptions and the plates that shape our planet. Haven't played yet? Take the quiz first and compare your score.
Play the quiz · 15 questions1. At the San Andreas Fault, the two tectonic plates mainly do what to each other?
Answer: Slide past each other horizontally
The San Andreas is a right-lateral strike-slip (transform) fault where the Pacific and North American plates grind horizontally past each other, the Pacific side moving northwest at roughly 20-35 mm per year.
2. On the Richter scale, each whole number step means shaking how much bigger?
Answer: 10 times
The Richter scale is logarithmic, so each whole-number step means a tenfold increase in the amplitude of the recorded seismic waves, while the energy released rises about 31-32 times per step.
3. Besides Pompeii, which Roman town was buried by Vesuvius in AD 79?
Answer: Herculaneum
Herculaneum was buried alongside Pompeii in the AD 79 eruption of Vesuvius, entombed under some 20 metres of pyroclastic material; nearby Oplontis and Stabiae were destroyed too.
4. The 1755 quake that devastated Lisbon struck on which Christian holy day?
Answer: All Saints' Day
The Great Lisbon earthquake struck around 09:40 on 1 November 1755, All Saints' Day, when churches were packed with worshippers; a tsunami and days of fire followed.
5. Which Hawaiian island sits over the hotspot today and has erupting volcanoes?
Answer: Hawaii, the Big Island
The Big Island of Hawaii currently sits over the Hawaiian hotspot and hosts the chain's erupting volcanoes, Kilauea and Mauna Loa, while older islands like Kauai have drifted northwest off the plume.
6. What mainly drives Earth's tectonic plates to creep across the planet's surface?
Answer: Slow convection currents in the hot mantle
Plates move as part of Earth's internal heat engine: slow convection in the mantle, driven by heat from the core and radioactive decay, carries the rigid plates along. Within that system, gravity forces called slab pull at subduction zones and ridge push at mid-ocean ridges do most of the work.
7. The moment magnitude scale, preferred today for big quakes, mainly measures what?
Answer: The total energy released by the rupture
Moment magnitude, introduced by Hanks and Kanamori in the 1970s, is based on seismic moment, calculated from rock rigidity, rupture area and average slip, so it reflects the total energy released. It avoids the saturation that makes the Richter scale unreliable above about magnitude 8.
8. The 1883 eruption of Krakatoa took place in which modern-day country?
Answer: Indonesia
Krakatoa sits in the Sunda Strait between Java and Sumatra, in what was then the Dutch East Indies and is now Indonesia. Its climactic explosions on 27 August 1883 destroyed most of the island and triggered tsunamis that killed roughly 36,000 people.
9. Most of San Francisco's destruction in 1906 was caused by what after the quake?
Answer: Fires that burned for days
After the magnitude 7.9 quake of 18 April 1906, fires fed by ruptured gas lines burned for about three days and caused roughly 80 percent of the property damage, destroying some 28,000 buildings. Broken water mains left firefighters almost helpless.
10. Mount St Helens, which erupted violently in 1980, stands in which US state?
Answer: Washington
Mount St Helens is in the Cascade Range of Washington state, and its 18 May 1980 eruption began with a huge landslide that unleashed a lateral blast, killing 57 people.
11. Which seismic waves travel fastest and reach a seismograph first after a quake?
Answer: Primary (P) waves
Primary (P) waves are compressional body waves that travel roughly 1.7 times faster than shear S waves, so they always register first on a seismograph. The time gap between the P and S arrivals lets seismologists calculate how far away the epicentre lies.
12. The Japanese word 'tsunami' literally translates into English as what?
Answer: Harbour wave
The Japanese word tsunami (津波) combines 'tsu' (harbour) and 'nami' (wave), literally 'harbour wave'. The name came from fishermen who noticed nothing unusual at sea but returned to find their harbours wrecked.
13. Which scientist proposed the theory of continental drift back in 1912?
Answer: Alfred Wegener
German meteorologist Alfred Wegener first presented continental drift in a lecture in Frankfurt on 6 January 1912, expanding it in his 1915 book The Origin of Continents and Oceans. Lacking a mechanism, his idea was only accepted in the 1960s with plate tectonics.
14. The strongest quake ever recorded, magnitude 9.5 in 1960, hit which country?
Answer: Chile
The magnitude 9.5 Great Chilean (Valdivia) earthquake of 22 May 1960 is the strongest ever instrumentally recorded. The megathrust rupture lasted about ten minutes and sent a Pacific-wide tsunami that killed people in Hawaii, Japan and the Philippines.
15. Which Roman writer's letters describe an eyewitness view of Vesuvius in AD 79?
Answer: Pliny the Younger
Pliny the Younger wrote two letters (6.16 and 6.20) to the historian Tacitus describing the AD 79 eruption of Vesuvius, which he watched from Misenum as a teenager. His uncle, Pliny the Elder, died during the event, and 'Plinian eruption' is named after the account.