Tomanowos - the rock that went through planetary collisions, megafloods, and idiocy

Last week I had the opportunity to face the rock with the most fascinating story on Earth at the AMNH:

Tomanowos, the visitor from the sky, also known as the Willamette meteorite. 
Supernovas spread throughout space the
iron produced in heavy stars. This ejected iron
ends up in particle nebulas that form stars and
protoplanets. [Image: NASA] 

Tomanowos is a rare 15,500-kg meteorite made of iron and nickel (Fe 91%, Ni 7.6%), originally found in the Willamette Valley, near Portland, Oregon. These Fe and Ni atoms formed at the core of stars that shattered the space with the sub-products of nuclear fusion when exploding as supernovas. These materials eventually formed the solar nebula that clumped together as protoplanets in the Solar System, and Tomanowos was part of the heavier core of one of these protoplanets

Vesta, a surviving protoplanet of the 
early Solar System. Due to their large
 size, protoplanets develop a differenciated 
density distribution with heavier elements like 
iron concentrated in the core. Tomanowos is an 
ejected piece of a protoplanet core like this. 
[EPFL/Jamani Caillet, Harold Clenet]
A protoplanetary collision 4 billion years ago sent a piece of that core back to space. Subsequent impacts made the orbit of this meteorite go across that of the Earth, at a speed of ~60,000 km per hour. As a result of this cosmic billiard, the meteorite landed on an ice cap in Canada around 20,000 years ago.

Over the following decades, the ice flow slowly brought Tomanowos southwards, towards a glacier lobe that was at the time blocking the Fork River in Montana. The glacial tongue piled ice across the river valley forming a 600-m barrier that impounded the enormous Lake Missoula behind. Tomanowos happened to reach the ice dam at the precise year when it collapsed, releasing one of the largest floods ever documented: the #MissoulaFloods that excavated the Scablands in Washington. This process is known as glacial outburst flooding and it still happens every few years in the Perito Moreno glaciar, for example. Except that the water discharge during the Missoula Floods is known to have been equivalent to a few thousand Niagara Falls. The research of the Missoula floods by Bretz and Pardee in the early 20th century led to one of the most significant paradigm shifts in recent geoscience: the recognition that catastrophic events can significantly contribute to landscape evolution.
Map of the Missoula Floods path, showing Lake Missoula 
(blue), the ice cap where Tomanowos landed (north of the 
lake outlet), and the inundated areas of Washington and 
Oregon (grey).
Source: Washington Univ.

Trapped in ice and rafted down the flood, Tomanowos crossed Idaho, Washington and Oregon along the Columbia River at speeds sometimes faster than 20 meters per second. While floating up on the flood waters near today's Portland, the ice case broke apart and the meteorite was dropped on the lake bottom. There are hundreds of such ice-rafted erratics (rocks that do not match the local geology, nor could be transported by rivers or glaciers) along the Columbia River. All are due to the Missoula floods.

As the flood ceased, the meteorite became exposed to the atmosphere. Over thousands of years, rain water mixed with iron sulfide inclusions producing sulfuric acid that gradually dissolved the iron in the exposed flat side of the rock:
These cavities were produced by acid dissolution of iron at the exposed side.
A few thousand years after the flood, the Clackamas arrived to Oregon and named the meteorite as the Visitor of the Sky, a heaven's representative that unified earth, water & sky. Did they know that nickel rocks come from heaven? Were they intrigued by the absence of a crater at the Meteorite site? This reminds us that pre-scientific cultures were not idiotic, or not more than us anyway.

To confirm the latter hypothesis, in 1902 a colonist named Ellis Hughes decided to literally move the iron rock to his own land to claim property. Moving a 15-ton rock a distance of 1200 m without being noticed is not easy, not even in Oregon, and it was at this time that the rock went severely mutilated. Hughes and his son labored for three back-breaking months in secrecy: 

As D. J. Preston hilariously explains, after finally
succeeding with the moving, Hughes built a shack around
the meteorite, announced he had found it on his property
and started charging twenty-five cents admission to view
the heavenly visitor.
Meanwhile, Hughes' neighbor started a lawsuit contending that the meteorite had, in fact, landed on his property. To buttress his case he showed investigators a huge crater on his land. The case was dismissed when a third neighbor reported a great deal of blasting only the week before.

IRONically, the legal owner of the iron meteorite turned out to be the Oregon Iron and Steel Company that was unaware of the meteorite in its land but soon hired a twenty-four-hour guard who sat on top with a loaded gun while the case was being appealed. They won the case in 1905.
The meteorite in the early 1900s, before being transported to the AMNH.

The @AMNH acquired the rock in 1906. Amazingly enough, the exhibition does not yet mention the Missoula Floods as a key part of the meteorite story, in spite of the wide geomorphological consensus (a note on a modeling paper of the floods linked here). 

The descendants of the Clackamas still keep the right to visit the meteorite and use it for rituals. 


Glacier retreat in southern Iceland

Looking at old pictures, I realise that I had a first-hand glance at the retreat of the Jökulsárlón glacier (S. Iceland) back in 2013. I took these two pictures from the same spot with an 18-years time lag. Although the first one is taken in August and accordingly shows less snow in the background mountains than the more recent one, the latter does show the glacier front retreated by about 3 km. I pasted the Landsat images for comparison.

Not that this is a surprise, really: 
But i had to share.
In the meanwhile, I found this other JAXA (Japan) link as well. 


Extreme Geodynamics at the Tsangpo Gorge

If you aim at understanding what shapes the surface of the Earth, the Tsangpo Gorge (Eastern syntax of the Himalayas) will inevitably become one of your favorite places.

This is the place where bedrock is
being eroded at the fastest
measured rate of nearly 1 mm/yr.
The uncommonly vertical valley
walls adopt this high angle to cope
by landsliding with the incision rates
produced by water. 
This is the place on Earth where one of the the highest bedrock erosion rates, the fastest tectonic uplift, and some of the highest topographic gradients have been measured. Every year, nearly 1 cm of very hard metamorphic rock is dig by the Tsangpo River, which descends from an elevation of >3000 m near the Tibetan plateau, to a mere 1000 m in less than 100 km. An average water discharge above 1400 m3/s, together with the pronounced slope, implies a huge erosion power.
Upstream from this gorge, there are widespread terraces and shore sediments of a lake that used to cover a few hundred kilometers of the river valley and impounded up to 800 km3 of water in a lake. What caused this impoundment is a matter of discussion: Only the tectonic uplift along the gorge? Or also an increase in landsliding from the valley flanks during the Pleistocene? Or glacial moraine accumulations?
The long duration of this competition between uplift and erosion (at least 10 Myr) implies that the region must be approximately in equilibrium, so uplift rates are presumably in the range of a cm per year, only comparable to the post-glacial isostatic rebound of Scandinavia.

A recent study of the infill of those lake sediments concludes that the steepening of the Tsangpo Gorge started about 2 to 2.5 million years ago as a consequence of a faster rock uplift: 
(A) Longitudinal river profile of the Tsangpo River, location of drill cores with observed depth to bedrock (vertical black bars), estimated depth to bedrock (yellow area), and reconstructed valley bottom before uplift of Tsangpo Gorge (dashed line). (B) Hillslope angles at the river flanks, specific stream power, and landslide erosion rates. (C) Erosion rates of close to 10 mm/yr are reflected in the age at which the minerals cooled down while being exhumed towards the surface. From Wang et al., 2014, Science. 
The extreme uplift and exhumation rates have been linked to a feedback effect of erosion on channelizing crustal rock towards the surface (the so called tectonic aneurysm; Montgomery & Stolar, 2006).

In contrast, other studies favor the role of glacial transport from the high surrounding mountains near the gorge in blocking the river with glacial moraines. This may have triggered megafloods sourced at impoundments formed by glacial dams (Lang et al., 2013, Geology), since some of the largest known outburst floods in the world have also been reported here.

Tsangpo Gorge
Hence, the competition between tectonic uplift and erosion at the Tsangpo encompasses many of the big conundrums in present geomorphology and geodynamics: the importance of episodicity in landscape evolution, the implications of the glacial ages on erosion rates, the possible effects of climate on tectonic deformation...


How do we know that the Earth has a core?

1. A typical depiction of the core
of the Earth.
Many of us have wondered, at some point of our lives, why the cartoons depicting the Earth as a watermelon with a missing portion always show this ball in the center named the 'core'. How do we know that a distinct 'body' is actually down there, 2900 km below the surface?

Let's see: we know the total mass of the Earth through its gravitational interaction with the solar system. In 1797, Cavendish [ref.1] measured the Gravitational constant G and the density of the Earth is ever since known to be about 5.51 times the density of water: nearly twice the average rock density we find at the surface.

In 1898, Wiechert suggested [ref.2] that this high Earth’s density could be explained by a core in the center made of nickel and iron (like many meteorites known at the time) surrounded by a shell, or mantle, of the lighter silicon-dominated rocks that we see in the surface.

2. Inge Lehmann was one of the key
discoverers of the inner core of the Earth
But only in 1906, Richard D. Oldham found that the increasing speed of seismic waves with depth within the Earth holds only down to 2890 km below the surface. Deeper than that, the mechanical waves (sound) propagate much slower (fig. 6), suggesting a different rock nature. Because this distinct material did not transmit shear seismic waves, it became clear that this core is liquid.

In 1936, Inge Lehmann found that the center of the core is indeed nearly-solid, since she detected weak shear waves travelling through it [ref. 4] using highly-sensitive seismometers in New Zealand. This has become known as the inner core.

3. Images of the tsunami following last week's earthquake in Chile.

Today, detecting the core down there has become a doable task for anyone. Last week's earthquake in Chile, for example, provides a great opportunity for you to check if Oldham did everything right. You only need to get seismograms from seismic stations around the world (many of these stations have their data publicly available), and sort the signals according to the distance from the station to the EQ's epicenter, using the same time of reference, like in this image:
4. Left: Each horizontal line is a seismogram of the Chile earthquake recorded at different locations of the planet (check USGS: 2015-10-16; Mw=8.3). Each seismogram is plotted according to the distance of the measuring station to the earthquake (vertical axis). The red circle shows the signal gap due to the outer core.
Right: Same image, with the identification of the arrivals of the different seismic waves. 'P' waves are the compressional waves, they are first to arrive all around the planet's surface.
The horizontal axis shows elapsed time, measured since the EQ occurred.
The vertical axis shows the distance from the measuring station to the EQ.
The red circle shows the region (around 110 degrees from the source) where the first seismic waves are not recorded. 

5. Seismic shadow produced by an imaginary
earthquake occurring at the north pole. The
outer core, due to its slower seismic velocity,
refracts the mechanical waves of the earthquake,
shadowing a vast region of the planet, as seen
in figure 4.
6. The velocity of seismic waves
changes with depth within the Earth.

In summary: the absence of wave reception in regions around 14,000 km (between 103 and 143 degrees) apart from the hypocenter demonstrates that there is a liquid core where seismic waves travel slow.
Isn't it amazing that nobody realized this before the 20th century?

Finally, remember that the outer core is where the magnetic field of the Earth is generated, by the thermal convection of conductive molten iron around a nearly-solid iron inner core. In fact the changes in the convection patterns in the outer core seem responsible for the rapid historical changes observed in the magnetic field. There is more about the magnetic field in this earlier post.

7. Convection in the iron-dominated outer core is
the most-accepted cause for the Earth's magnetic field.
Update 2015-11: a new study finds that the core (and thus the magnetic field) was formed by the gradual cooling of the Earth only 1 to 1.5 billion years ago.

Update 2015-12: Geophysicists call it the new core paradox: They can't quite explain how the ancient Earth could have sustained a magnetic field billions of years ago, as it was cooling from its fiery birth. Now, two scientists have proposed two different ways to solve the paradox. http://ow.ly/W3eQX

References (thank you nuclearplanet):
1. Cavendish, H., Experiments to determine the density of Earth. Philosophical Transactions of the Royal Society of London, 1798, 88, 469-479.
2. Wiechert, E., Über die Massenverteilung im Inneren der Erde. Nachr. K. Ges. Wiss. Goettingen, Math-Kl., 1897, 221-243.
3. Oldham, R. D., The constitution of the interior of the Earth as revealed by earthquakes. Q. T. Geol. Soc. Lond., 1906. 62, 459-486.
4. Lehmann, I., P'. Publ. Int. Geod. Geophys. Union, Assoc. Seismol., Ser. A, Trav. Sci., 1936, 14, 87-115.


Conferencias de divulgación geocientífica (50 aniversario del ICTJA)

Con motivo del 50 aniversario de nuestro instituto, cuatro investigadores del ICTJA participamos en el ciclo de conferencias divulgativas en Barcelona: "Las Ciencias de la Tierra en nuestra vida cotidiana", dentro del Cicle Dilluns de Ciència del CSIC-Catalunya.

Lugar: (mapa)
Sala d’Actes de la Residència d’Investigadors,

La conferencias de divulgación son los siguientes lunes:

2 Novembre, 18:30 h,
Charles Darwin, Lord Kelvin, els radioisòtops i el concepte de Temps
Dr. Santiago Giralt

9 Noviembre, 18:30 h
Tambora, 200 años de la erupción que cambió el Mundo
Dra. Adelina Geyer

16 Noviembre, 18:30 h
Megainundaciones, placas tectónicas y la formación del relieve terrestre
Dr. Daniel García-Castellanos

23 Novembre, 18:30 h
Interacció radiació-matèria per a estudiar-ho gairebé tot: nanomaterials, minerals exòtics, obres d’art, cadàvers,...
Dr. Jordi Ibáñez


Continental-scale evolution of topography and river networks. Tectonics and climate shaping Eurasia

[This post is about our recent publication on PLOS ONE]

How much does the erosion and sedimentation at the Earth’s surface influence on the patterns and distribution of tectonic deformation? This question has been mainly addressed from a computer modelling perspective, at scales ranging from local to orogenic. In the PLOS ONE paper published today, we present a model that aims at understanding this phenomenon at the continental scale, looking at the feedbacks between continental enlargement and climate aridification during the collision of continents.

60-million-year indentation of a continent from the south 
(at 50 mm/yr). 

Left: Topography and areas with precipitation
higher than 400 mm/yr (red shading). Note the 
orographic rainfall developing at the southern flank 
of the growing plateau. Wind blows from the southeast 
(towards the upper left corner).

Right: erosion and sedimentation rates, and
contours of crustal thickening rate due to tectonics. 

By Garcia-Castellanos & Jimenez-Munt, PLOS ONE, 2015. 
+ info here.

We couple a thin-sheet viscous model of continental deformation with a stream-power surface transport model. The model also incorporates flexural isostatic compensation that permits the formation of large sedimentary basins and a precipitation model that reproduces basic climatic effects such as continentality and orographic rainfall and rain shadow. We calculate the feedbacks between these four processes acting at different scales in a synthetic scenario inspired and scaled by the India-Asia collision. The model reproduces first-order characteristics of the growth of the Tibetan Plateau as a result of the Indian indentation.

Note that the southern continent (the indenter, India)
is chosen fixed to our reference frame, whereas
 the northern continent (Asia) is moving southwards). 

The initial topography is flat with small random noise
forming a network of lakes. 
The tectonic indenter in
the southern boundary represents India, while a rigid
block fixed around x=2500km represents the Tarim Basin. 

Wind blowing from SE at 7 m/s (relative humidity=1).
Red shading indicates orographic precipitation.

The continental deformation adopts a thin-sheet tectonic
+ info here.
What these simulations show is that, at large space and temporal scales, the climate dryness that develops in continental interiors triggers the trapping of sediment in closed basins within the continent, instead of exporting it to the continental margins. In the left panel you can see a large intramountain basin (comparable to the Tarim Basin) developing within Asia when a hard lithospheric region in predefined within the continent. The amount of sediment trapped in it is very sensitive to climatic parameters, particularly to evaporation, because it crucially determines its endorheic/exorheic drainage. We identify a feedback between erosion and crustal thickening leading locally to a <50 at="" climatically-enhanced="" concentrated.="" corners="" deformation="" flank="" growing="" in="" increase="" indenter="" is="" of="" orographic="" p="" place="" places="" plateau="" precipitation="" preferentially="" rates="" specially="" syntaxes="" takes="" the="" this="" upwind="" where="">
We hypothesize that this may provide clues for better understanding the mechanisms underlying the intriguing tectonic aneurysms documented in the Himalayas. At the continental scale, however, the overall distribution of topographic basins and ranges
seems insensitive to climatic factors, despite these do have important, sometimes counterintuitive effects on the amount of sediments trapped within the continent. The dry climatic conditions that naturally develop in the interior of the continent, for example, trigger large intra-continental sediment trapping at basins similar to the Tarim Basin because they determine its endorheic/exorheic drainage. These complex climatic-drainage-
tectonic interactions make the development of steady-state topography at the continental scale unlikely.