Iceland: Ridge Hotspots
1. Zoom from the Maldives to Iceland
2. Iceland is a Geologist’s paradise.
a. Like a giant geologic wonderland, with mountains, canyons,
waterfalls, geysers, and most importantly, volcanoes and glaciers.
b. It even has volcanoes under glaciers.
c. To start, it is the only place on the Earth where you can walk right
down along a mid-ocean rift above land. [show photo, diagrams]
i. It is a hotspot that is on the mid-Atlantic ridge
ii. There are many other hotspots at ridges (puzzling??), but this
is the only place you can walk down the ridge.
iii. Imagine if you took the Galapagos Rift we saw in Lecture XX
and brought it up to the surface. Eruptions are intermittent,
but sometimes the rifts erupts in lava.
3. Iceland has more than 30 separate active volcano systems
a. In March 2010, a volcano in Eyjafjallajökull started erupting; shut
down air traffic in parts of Europe for weeks.
b. Hekla – one of the most active volcanoes in Europe
i. Erupted 20 time in the last millennium
ii. Also large eruptions about 3000, 4000, 6000, and 7000 years
ago. The ash is found across parts of Europe, and is a good
archaeological time marker.
iii. Following a big eruption of 1104, and for many hundreds of
years, Hekla was considered by many to be the gateway to hell
(as in the 1585 Ortelius map)
c. Sometimes new volcanoes are born, as with the emergence of Surtsey
in 1963. Birth of an island – still off limits to people, to see how an
island becomes biologically populated.
d. Volcanic regions heats the water underground:
i. geothermal baths
ii. Geysers: original is “Geysir”!!!
e. Volcanoes are both blessing and a curse.
i. Provide heat for most of the island; hot baths; geothermal
electricity is about 20% of Island’s need.
ii. But can be destructive, as in 1973, when a volcano erupted
right behind the town of Vestmannaeyjar on the island of
Heimaey, off the coast of the main island. (not far from Surtsey)
iii. The volcano’s ash and lava crushed most of the village, but
people cooled it with hoses, and stopped the flow, and the lava
extended out into the harbor, actually improving the harbor!
iv. In general, however, Iceland is a rough place to live: cold
climates and poor soil. It takes a hearty people to survive here --Vikings!
v. Vikings began to settle in the late 800s, as the world was
entering the a warm period known as the Medieval Warm
Period (sun was giving off a tiny bit more energy).
1. The sea around Iceland had been frozen for half the
year (and would be again during the Little Ice Age).
2. Still carry some of the old Norse traditions, that used to
hold throughout scandanavia. People still take the name
of their father as their last name.
3. Magnusson is “Son of Magnus;” Ragnarsdottir is
“daughter of Ragnar”
4. Very few different names in the phone book!
f. Sometimes the volcanoes erupt under the glaciers, melting a lot of ice
quickly, as in 2011 with Grímsvötn volcano, located under the thick
ice of one of Europes largest glaciers, the Vatnajökull.
g. This eruption was in the same region as the famous 1783-4 eruption
of Laki fissure and the adjoining Grímsvötn volcano; poured out
14 km3 (3.4 cu mi) of basalt lava and clouds of poisonous hydrofluoric
acid/sulfur-dioxide compounds
i. killed over 50% of Iceland's livestock population, famine killed
approximately 25% of the population.
ii. Laki eruption killed over six million people globally, making it
the deadliest volcanic eruption in historic times. The drop in
temperatures caused crop failures in Europe, droughts in India,
and Japan's worst famine.
4. Iceland has glaciers located in many regions about the island, but most of the
ice is located in one large ice cap, Vatnajökull, which has over 3000 km3 of
ice in it.
a. About 10% of Iceland is covered with glaciers.
b. When an eruption occurs underneath the glacier, an enormous
outrushing of water can occur – a jökulhlaup.
c. The melting of glaciers also creates some spectacular waterfalls
i. Like the multi-stepped Gullfoss (Golden Falls), or Dettifoss
5. No geologist doubts that Iceland is a hotspot, with an enormous outpouring
of lava at this one location. But there is a huge debate as to what is actually
causing it.
a. Seismic tomography does show a region of warm rock extending
down into the mantle, but it is not clear how far down it goes; might
not go all the way down to the top of the core, as with Hawaii
b. The hotspot also doesn’t seem to be “hot:” the surrounding crust
doesn’t have unusually high heat flows, as with Hawaii. There is just a
whole lot of lava flowing out!
c. However, there IS a large gravity anomaly – the whole crust in that
regions seems to be lifted up from below, which is supportive of the
idea of a mantle plume there.
d. One hypothesis – it is a “wet spot,” a region of slightly higher water
content in the mantle rock, which lets it melt more easily.
e. Or, it could be former ancient ocean crust that got subducted the last
time the Atlantic closed up, and is still floating around down there. It
melts more easily, so as it is slowly pulled toward the ridge, it melts
more voluminously.
f. One thing for certain, when the Iceland hotspot first appeared, it had
an effect even greater than changing European climates or shutting
down airports; it tore off a piece of Europe!
i. When Pangaea started breaking up, Greenland was part of
Europe, directly adjacent to Scandinavia.
ii. The Mid-Atlantic ridge ran up between Labrador (Canada) and
Greenland, through what is now the Labrador Sea. The first
outpourings of lava were about 65 million years ago. It came
out in several areas, and some people hypothesize the plume
was under Greenland and came out in several locations.
iii. About 35 million years ago, however, the bulk of the Iceland
hotspot lava came out between Greenland and Scandinavia,
(remains seen on both sides of the Atlantic there), and the MidAtlantic ridge jumped!
iv. Like perforating a piece of paper.
v. Labrador sea is now extinct, though still gets a few
earthquakes now and then.
vi. Iceland’s oldest observed lava is 20 million years old.
1. Q? Is the ridge there because of the hotspot, or is the
hotspot there because of the ridge.
2. Lab experiments (corn syrup) and computer
simulations show that either could be the case.
3. Won’t know for 10s of millions of years, perhaps.
vii. It may be the case that when a supercontinent like Pangaea
breaks up, mantle plumes like Iceland are responsible for
determining exactly where the plates break.
6. Top 5:
a. Tristan de Cunha – first erupted when SAmer and Afr broke up
i. May have triggered the separation
ii. Seen in Parana (Brazil) and Etandeka (Angola/Namibia) flood
basalts that are >135 Ma old.
iii. Tristan is now at the ridge, still active
b. St. Peter and St. Paul rocks – islands at the equator in the Atlantic
Ocean. – Faulting has pulled the crust off of the mantle, exposing
mantle rock (peridotite). In fact, only place where the mantle is
exposed at the surface.
c. Azores – sit at the junction of 3 plates – NAmer, Eurasian, African.
d. Afar – sits at the end of the Red Sea, and may be responsible for
opening it. More later (in last lecture).
Questions:
1) Why do Iceland’s volcanic eruptions affect Europe more than North America?
2) Iceland gets a lot of its electricity from geothermal and hydroelectric
resources. Why doesn’t it have any resources of coal or oil?
Hawaii should go before Iceland - it is the quintessential hotspot.