Download Erta Ale (Ethiopia): Lava Lakes

Erta Ale (Ethiopia): Lava Lakes
1. Zoom from the Galapagos Islands to Erta Ale, Ethiopia.
2. Last lecture looked at the volcanoes at the mid-ocean ridges and at the
Galapagos Islands. Galapagos – hotspot volcanism at a mid-ocean ridge. Here
we will look at one particular volcanic Geologic Wonder that can form under
unique situations: a lava lake.
3. In Lectures 1 and 2 we looked at volcanoes that occur at subduction zones,
which tend to be explosive.
a. Lots of water, brought in during subduction: phreatic explosions
b. Composition is intermediate between continent and ocean crust – rich
in silica (“gummy”)
c. In Lecture 3, we saw a different kind of volcanism; basalt, which is
more fluid, less explosive. Mostly erupts at the ridges, under water,
but in some cases, like at the Galapagos islands themselves, the basalt
flows out, in gentler eruptions (not explosive).
4. In very rare cases, the lava will slowly feed into a crater, and churn and
bubble away like a seething cauldron. These are called lava lakes. In fact,
there are only 5 in the world. The oldest and longest running current lava
lake is in Ethiopia in a volcano called Erta Ale.
a. Located right near the bottom of the Red Sea, in northern Ethiopia.
This is not a coincidence. There is an enormous amount of volcanic
activity in this region, known as the Afar hotspot, and it is responsible
for pushing Arabia away from Africa and opening up the Red Sea.
b. [We will talk more about the opening of the Red Sea when we talk
about the Dead Sea, in Lecture 29]
c. [We will talk more about hotspots when we talk about Hawaii in
lecture 24 and Iceland in lecture 27]
d. Erta Ale sits at the north end of the East African Rift Valley [and we
will talk more about that in the last lecture, Lecture 36!!]
e. Erta Ale is the name of both a range of many volcanoes that occur
along a line, and also the name of the most active volcano there.
f. It sits in a very unusual place, the Danakil Depression, that is actually
below sea level in many places, by up to 500 feet. As a result, though
Erta Ale is a large volcano, it reaches a height of only 600 m (2000 ft)
above sea level.
g. But is it very wide – 50 km wide – with an elliptical summit caldera
that is 1 mile wide (1.6 km) and contains many smaller pit craters. It
is in these pit craters that the bubbling lava lakes can be found.
h. This is called a “shield volcano,” and is the result of low-viscosity lava
that can flow outward for great distances.
5. Lava lakes are rare because they tend not to last very long – the lava drains
out of the caldera at the top or cools and hardens quickly. You need to have a
continuous supply of lava to maintain a lava lake for a long time. For Erta Ale,
it has been a continuous lava lake for more than 100 years!! (since 1906).
a. The activity is not always at a continuous level, however! In 2005
through 2007 there was a significant increase in activity!
b. Several fissures opened up, meters wide (one swallowed up a camel!)
and lava eruptions spread out across more than 300 km2.
c. Lava overflowed the lake again in 2010.
d. It is presently (2011) possible to drive with 4WD vehicles to within
7km W of the summit of the Erta Ale. The summit can then be reached
on foot in less than 3 hours. Local Afar tribesmen organize transport
of material or even tourists using camels. Numerous tour operators
can organize travel into the area, often combining visits to Erta Ale
with visits to the colorful nearby hot springs at Dallol Volcano. By
early 2011, numerous simple stone-walled huts had been erected on
the W rim of Erta Ale. Similarly, huts had been built at the parking
area.
e. The amazing Dallol hot springs are a result of sulfur and potassium
salts, colored by various other elements. We will see more of them in
Lecture 25, on Yellowstone.
f. Some of the lava flows are in the form of obsidian, a black glass.
g. There are terrible fumes that have the rotten-egg smell that shows the
presence of hydrogen sulfide.
h. Unfortunately for the people who live there, the region is so hot and
there is so little water that people actually collect the water from the
volcanic steam.
i. They build a wall around the fumarole and cover it with sticks
and leaves.
ii. The steam condenses on the leaves as water and they collect it.
iii. However, the steam contains many metals, some toxic, and
lifestock sometimes die from drinking this water, so tests are
being developed to be able to determine the safety of the
water.
6. Lava lakes consist of a liquid rock that is constantly churning because the top
part keeps cooling, hardening, and sinking back in and remelting.
a. The lava is about 1200C, too hot for anyone to be near for any
extended period of time.
b. One remarkable aspect is that it closely resembles the process of plate
tectonics.
c. As the surface crust of the lava lake begins to cool and harden, it
becomes heavier than the liquid below, and it will bend, crack, turn
sideways and sink back down into the boiling vat: just like a
subduction zone such as the one next to Japan that we saw in Lecture
2.
d. As this happens, the crust is pulled apart in places, and new lava
comes up from below to form new crust, just like at mid-ocean ridges
such as the Galapagos Ridge.
e. There are even places where two pieces of crust slide past each other:
This is called a transform fault. One of the most famous of these is the
San Andreas fault, which separates the Pacific Plate from the North
American Plate (LA is actually not in North America, geologically
speaking!).
7. Lava lakes are very important for one other geological reason: they are as
close as we get to seeing what the earliest period of Earth’s history was like.
a. This is especially true for Erta Ale: the Danakil Depression is one of
the driest and hottest places on earth, regularly reaching over 115F in
the summer with no rainfall.
b. The earliest Earth was extremely hot, with no water (too hot for water
vapor to condense to form oceans)
c. The heat came from many sources (impacts of proto-planets;
radioactive decay of short-lived isotopes; finally the impact of a Marssized planet that ejected material that came back together to form the
moon). Following the impact of the proto-Moon, 40-90 Ma after the
formation of the solar system, Earth’s mantle would have been mostly,
if not entirely, molten.
d. Surface would have been violently volcanic, with pieces of the crust
continuously sinking back into a molten mantle and remelting.
e. Earth’s mantle hardened and crystallized from the bottom up, so the
top part would have remained molten for many tens of millions of
years.
i. Even now, there is a layer of rock in the mantle
(asthenosphere), just beneath the plates, that is very close to
its melting temperature!
f. Eventually, the surface, cooling off into space, got cold enough for
water to condense and rain out of the atmosphere to form the ocean.
i. Just like at Erta Ale, where the fumarole and steam vents
contain water, but on a giant scale! Much, probably most, of the
water that formed our Earth’s ocean came out of the earth as
steam through volcanoes!
g. Unfortunately, we have no record of this time. The rocks that formed
at the surface kept sinking back into the molten mantle and remelting,
so there are no rocks in existence today from that earliest time.
h. But looking at and examining lava lakes gives us some idea of how our
planet started out, 4.5 billion years ago: hot, dry, and violently
volcanic.
i. The only other place we might get a sense of our earliest history is by
visiting the most volcanic place in the solar system, Jupiter’s moon Io.
Heated by tidal friction from Jupiter and with no atmosphere, Io is just
a giant ball of volcanoes, with over 100 active and erupting at any
given time.
j. Incidentally, Erta Ale meets the conditions for many people’s
perception of Hell!
i. The southernmost pit of Erta Ale is referred to as “the gateway
to Hell” by local Ethiopians.
ii. And the 2010 Hollywood movie “Clash of the Titans” shows the
Erta Ale lava lake when Perseus travel to the Underworld!
8. Top 5 (This one is easy, because there really are only 5 lava lakes on Earth!)
a. Nyiragongo (Dem. Rep. of Conga) – farther down the African Rift
valley, also a result of Africa splitting apart. Hade a huge lava lake up
until 1977 (600 m deep!), but it drained in an hour during an
eruption. Flows traveled at up to 60 mph!! Currently has a lava lake
again. Has erupted 34 times since 1882. Last big eruption was in 2002
– 47 people died from asphyxiation from CO2.
b. Kilauea (Hawaii) – two separate lava lakes: Halemaumau, and Pu’o
O’o.
c. Marum Crater, island of Ambrym (Vanuatu) – named by Captain Cook,
1774. Crater sits in a large caldera (100 km2)
d. Erebus (Antarctica) – persistent low-level activity, not far from
McMurdo station.
Questions:
1) Why do you think that most volcanoes do not have a lava lake associated
with them?
2) It can take 10s or even 100s of years for a lava lake to completely solidify if
no new magma is added. Why do you think it takes so long?