2016-10-04

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



Last week, at the at the AMNH museum in NY, I had the opportunity to face the rock with probably the most fascinating story on Earth:

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 eventually form
new 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.

As in other metal meteorites, 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 at the end of their lives. These materials eventually formed the solar nebula that clumped together as protoplanets in the Solar System, and Tomanowos was part of the heavy core of one of these protoplanets, where the heavier metals were accumulated. 


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 bottom of the flooding waters. Hundreds of other ice-rafted erratics (rocks that do not match the local geology, nor could be transported by rivers or glaciers) have been found along the Columbia River. All are souvenirs of 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 of the exposed 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 today anyway.

To confirm this 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 1,200 m without being noticed is not easy, not even in Oregon. 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.
It was during this transport that the rock sadly underwent severe mutilations.
Unimpressed by this deployment of idiocy, Hughes' neighbor fabricated 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. But the descendants of the Clackamas still keep the right to visit the meteorite and talk to the visitor who brought the sky, the water, and the Earth together.