July 1928. A Miniature. Meteor Crater. A Circular, Crater-like Depres sion in Esthonia Bears at Least. Superficial Resemblance to the. Famous Crater in Arizona.
July 1928
45
SCIENTIFIC A M E RICAN
A Miniature Meteor Crater A Circular, Crater-like Depres sion in Esthonia Bears at Least Su perficial Resemblance to the Famous Crater in Arizona By ALBERT G. INGALLS
G
EOLOGISTS of the University of Dorpat in the small country of Esthonia lying between Russia and Scandanavia, on the eastern shore of the Baltic Sea, are endeavoring to discover the mysteri ous origin of a peculiar geologic feature on the nearby island of Oesel or Saare maa. (See map on page 43.) There, 14 miles northeast of the ancient city of Arensburg, or Kuresaar, in the immediate vicinity of the little village called Kaali or Salle, is a nearly circu lar depression like a crater, not more than 300 feet in diameter and sur rounded by a wall or rim which stands 15 or 20 feet above the level of the plain in which the strange depression occurs. The question which intrigues the local geologists is whether this anoma lous feature of an otherwise fiat,feature less landscape is simply an ordinary case of ground water solution of the rock with the caving in which com monly produces what are known in the American middle west as "sink holes," or whether we have here another though smaller "Meteor Cra ter" like the famed mile-wide depres sion in Arizona which is now being probed by means of a shaft, for the large meteoric aggregate which is thought to have excavated the crater in its fall. These two theories-the sink-hole
What forces tilted these strata? See map, SCIENTIFIC AMERICAN, July 1926, page 53
The lake is 14 feet deep, but it does not occupy all of the crater,
From a geological point of view its presence in the bottom of the depression is not significant
theory and the meteoric crater theory -coincide with two of the three theories originally advanced to account for the Arizona crater, and have been men tioned by the well-known geologist, Professor Alfred Wegener of the Uni versity of Graz, Austria, the same Pro fessor Wegener whose theory of drift ing continents has been widely dealt with in popular journals. The third or volcanic theory of the origin of craters has not been introduced in this case, because there are no signs of vol canic activity within hundreds of miles of Esthonia. Nor does the glacial mo raine, kettle-hole hypothesis seem to fit the circumstances.
,..... HE particulars of the description of J the crater on the island, which forms a part of Esthonia, were furnished by Mr. Konstantin Komets of Reval, capital city of that nation. The sur face soil, he states, is black earth with clay beneath, then sand, reaching in all to a depth of about 10 feet. Below this This variety of rock is is dolomite. closely allied to limestone, being com posed of the carbonates of lime and magnesia. This renders it necessary to take very serious account of the sink-hole theory, for dolomite, like limestone, is soluble in ground water and it would not be far-fetched to attribute the origin of a crater to the same agency which often dissolves out limestone and brings about the forma tion of the familiar sink-holes which sometimes engulf whole fields when the fall of the unsupported surface strata suddenly takes place. There are, however, several other features which seem to provide a peg on which to hang, at least tentatively, the meteoric theory. The crater, so far as its actual depth is known, ignoring any silting up which may have taken place subsequent to its original formation, extends to 30 feet· below the top of the exposures of dolomite, the total thick-
© 1928 SCIENTIFIC AMERICAN, INC
ness of which our correspondent does not specify. Under this dolomite a de posit of dolomite powder mixed with lar ger stones has been found. This, taken in conjunction with the stated facts that the rocks of the crater's rim are tilted up as if resulting from the impact of a projectile, as are some of those in the rim of the Arizona crater, and secondly, that the. rim of the crater stands 20 feet higher than the outside level of the plain, constitute a mass of evidence which demands further consideration of the hypothesis of meteoric origin. Within a distance of half a mile, as shown by the accompanying contour map furnished by Mr. Komets, there are 12 or more smaller craters ranging from 100 feet down to 15 feet in di ameter. It would seem that, if the main crater owed its origin to the same events which excavated the colony of small craters, and if this was truly the impact of a swarm of meteorites, it ought to be possible to settle the ques tion by exploring a small crater.
Coutte£y M.i.niD1 Ik-pMtmcnt. Eathonia
MAP OF THE CRATER Contour interval is one meter. A colony of small craterlets is indicated at one side
