WEEK 13 - Odd Earth Happenings Flashcards
What happened in Lake Nyos in 1986?
On August 26, 1986, 1,700 people and thousands of animals in the valley below Lake Nyos, Cameroon mysteriously died in their sleep.
After the event, the lake developed a strange orange color.
What caused the mysterious deaths near Lake Nyos?
Likely cause: Limnic eruption.
Carbon dioxide (CO2), trapped at the bottom of the lake, was suddenly released, suffocating people and animals.
The eruption of CO2 was triggered by a disturbance in the lake, releasing large amounts of gas all at once.
What is the volcanic connection to Lake Nyos?
Lake Nyos is located in a crater of a dormant volcano in a failed rift arm that formed during the opening of the Atlantic Ocean.
The volcano itself has been dormant for 400 years.
The 1986 disaster was not caused by any eruption of lava or pyroclastic debris, but rather by a limnic eruption of CO2.
What is the depth and composition of Lake Nyos?
Lake Nyos is 1 km wide and 200 m deep.
The upper 50 metres of water are fresh.
Below the 50-metre mark, the water becomes salty, due to sodium-rich volcanic fluids from the underlying magma chamber.
Why is Lake Nyos considered a “gas time bomb”?
The lake quietly accumulates large quantities of carbon dioxide (CO2) at the bottom, fed by an underlying magma chamber.
As long as the lake remains undisturbed, the CO2 is confined to the bottom.
What caused the disturbance in Lake Nyos that led to the gas release?
Carbon dioxide accumulated at the bottom of the lake until it could no longer be contained.
The CO2 rapidly escaped to the surface, creating a plume.
How did the gas release from Lake Nyos affect the area?
The carbon dioxide being denser than air, flowed close to the ground, suffocating victims up to 25 km away.
The water from the lake floor, which contained dissolved reduced iron, contributed to the orange colour after oxidation.
How has the threat of a similar disaster at Lake Nyos been addressed?
A lakewater piping system has been installed to allow long-term release of small amounts of carbon dioxide from the lake bottom.
This helps reduce the buildup of carbon dioxide, preventing a future disaster.
What is the Racetrack Playa?
Located in Death Valley, California.
A dry desert lake bed with loose dolostone boulders.
Boulders weigh up to 320 kg and rest on the lakebed.
Why is the Racetrack Playa known for strange rock behavior?
Some boulders are associated with long furrows on the surface.
Boulders are found hundreds of meters from the edges of the lake.
Some have moved up slight inclines, indicating gravity is not the only force involved.
The movement of these rocks was not observed until recently.
What causes the movement of boulders in Racetrack Playa?
Furrows show boulders mostly move northward, matching the wind direction.
GPS trackers were used to track their movement.
In winter, water on the playa freezes at night, forming a thin layer of ice.
This ice helps move the boulders.
How does the ice contribute to the movement of the boulders in Racetrack Playa?
When the ice melts, it breaks up into thin sheets.
These mini ice floes are moved by the wind, pushing the rocks across the slick surface.
After the ice and water evaporate, the rocks appear stranded on the dry surface
What is a mimetolith?
Natural geologic feature (e.g., rock outcrop, rock specimen, mineral) that resembles something else (e.g., animal, plant, or man-made item).
It’s a product of pareidolia (the tendency to see familiar shapes in natural objects).
Where can mimetoliths be found?
A museum in Chichibu, Japan, called Chinsekikan (Hall of Curious Rocks), devoted entirely to mimetoliths.
The museum specializes in jinmenseki, rocks that resemble human faces.
What are concretions?
Bodies of cemented sediment, often found in marine sediments with abundant organic matter.
They are commonly round or irregular in shape.
How are concretions formed?
When bacteria eating organic matter (containing carbon) release bicarbonate into the pores of the sediment.
The bicarbonate causes minerals to precipitate and cement the sediment together, forming a concretion.
How does the nucleation of concretions occur?
Bicarbonate combines with dissolved calcium in porewater to form calcite crystals (calcium carbonate).
These crystals cement sediment grains together, forming a concretion.
What role does a nucleus play in concretion formation?
Cementation is often localized around a nucleus, such as a fossil.
The nucleus helps form discrete bodies of cemented sediment, like around a fish or ammonite shell.
Why do concretions stand out on eroded surfaces?
Concretions are more resistant to weathering than the rocks around them.
When the host rock erodes away, concretions are left behind on the surface.
What misconceptions exist about concretions?
Some people mistakenly believe concretions are fossils or signs from gods or extraterrestrials.
Example: The “Fossil pumpkin patch” in Argentina is actually just an erosion surface exposing concretions.
What shapes can concretions take?
Unusual shapes due to differences in carbonate mineral precipitation and sediment type.
Examples of concretions shapes
Turtle stone: Calcite fills cracks in the concretion.
Fossil finger: The weathered rind of a concretion partially flakes off.
Fertility figure: Small concretions grow into each other.
Why do concretions sometimes form unusual shapes?
Local differences in carbonate precipitation and sediment type influence how concretions develop.
What is Bunyan’s Burger?
A large concretion exposed by erosion.
Found in North Coyote Buttes, Northern Arizona.
Split and eroded along bedding planes of cemented strata.
