This EarthCache will take
you to a roadside Historical Monument on Highway 4 highlighting the
rare meteor impact outside of Estherville, IA.
~Meteoric
Nights over an Iowan Prairie~
On most clear, moonless nights, patient skywatchers can see a
meteor, a streak of light produced by a piece of interstellar
material entering the Earth's atmosphere at high speed. If the
piece is large enough, it may actually fall to the ground and then
is called a meteorite. Iowa's largest meteorite impact occurred in
southern Pocahontas County, just north of Manson, 74 million years
before the state was inhabited. The second largest meteoric impact
occurred near this site.
Residents of Estherville in Emmet County received an
extra-terrestrial visitor at 5:00 p.m. on May 10, 1879. An
exploding meteorite roared to Earth along a seven-mile path from
south of Superior in Dickinson County to north of Estherville. When
it struck it buried itself 15 feet in the ground. Three large
fragments (weighing 431, 152, and 101 pounds) and hundreds of
smaller pieces were recovered. A monument near Estherville
commemorates the event.
Portions of the meteorite are on display in the Estherville
Public Library, the Smithsonian Museum of Natural History and the
Naturhistorisches Museum in Vienna Austria.
Analysis of the meteorite fragments indicated that several large
masses of a total weight of over 700 lb. (317.5kg) impacted the
ground. The two largest weighed approximately 437 lb. (198.1kg) and
151 lb. (68.5 kg) respectively, and hundreds of small fragments of
nickel iron fell, after the appearance of a brilliant fireball. . .
. analysis of metal, 9.0% Ni, 9.0 ppm Ga, 52.3 ppm Ge, 2.7 ppm Ir.
The meteorite fragments were classified as Mesosiderites.
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External view |
Internal (cut)
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Mesosiderites are a class of stony-iron meteorites consisting of
about equal parts of metallic nickeliron and silicate. They are
breccias with an irregular texture, silicates and metal occur often
in lumps or pebbles, as well as in fine-grained intergrowths. The
silicate part contains olivine, pyroxenes and Ca-rich feldspar, and
is similar in composition to eucrites and diogenites.
Magnification of 160X in cross polarized light
with the addition of a 1/4 wave plate.
They are a rare type of meteorites, until now (February 2006)
only 86 are known, and only 7 of these are observed falls. On the
other hand, some mesosiderites are among the largest meteorites
known. At Vaca Muerta in the Atacama desert in Chile, many
fragments were found in a large strewnfield, with a total mass of
3.8 tons. They were first discovered in the 19th century by ore
prospectors. They mistook the shiny metal inclusions for silver and
thought they had found the outcrop of a silver ore. Only later an
analysis was made and nickel-iron found, and the true nature as a
meteorite was established.
The most recent fall of a mesosiderite occurred at Dong Ujimqin
Qi in China, on September 7, 1995, where three large pieces with a
total mass of 129 kg fell. The fall of the Estherville mesosiderite
in Iowa, USA, occurred on May 10, 1879. After a brilliant fireball
had been seen, a shower of several large masses and many small
fragments fell, totalling 320 kg. Also the fall at Lowicz in Poland
on March 12, 1935, yielded many (more than 50) fragments with a
total weight of 59 kg. The other observed mesosiderite falls
occurred in 1842 at Barea (Spain), in 1880 at Veramin (Iran), in
1933 at Dyarrl Island (Papua New Guinea), and at Patwar (India) in
1935. The legendary Chinguetti meteorite is also supposed to be a
mesosiderite.
The Estherville Public Library proudly displays
fragments of this meteorite.
Library hours are:
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M 10-8 |
T 10-6 |
W 10-6 |
Th 10-8 |
F 10-5 |
Sat 10-1 |
Logging requirements for this
EarthCache are as follows:
1. Please post a photo or yourself and gps
and/or gps at the monument.
2. Please post a photo of one of the fragments at the Library.
Hours are posted.
3. Please describe the colour and appearance of one of the
meteorite fragments on display, and forward in an e-mail.
Thank you and please enjoy a rare occurrence
over Iowa’s Prairies.