According to the restorers who regularly monitor the condition of the main decoration of Palace Square, it will last at least another 300 years. However, St. Petersburg geologists have doubts about the validity of these figures. What are the chances that the process of destruction of the column will not accelerate literally before our eyes?
The thirtieth of August 1832 was marked by a momentous event. The entire city of St. Petersburg gathered to witness the raising of the column created in honour of the victory of Alexander I over Napoleon. Spectators occupied the entire square, windows, and roof of the General Staff Building. Even Tsar Nicholas I and the entire imperial family came. The monolith weighing 613 tons was brought upright very quickly, even by today’s standards, in just 1 hour and 45 minutes with the participation of almost 2,500 soldiers and workers.
However, in the early years, the citizens were afraid to approach the new monument and preferred to bypass the granite boulder in a wide arc. Everyone knew that the pillar and the figure of an angel were not fixed in any way and were held in their place only thanks to precise calculation, their weight, and gravity. The situation was aggravated by talks that allegedly someone had seen the monolith swaying on a windy day. Fighting the rumours, the project architect Auguste Montferrand walked around it with his dog every evening until his death, to prove the safety of the main symbol of the city.
Over time, residents of the northern capital ceased to fear the collapse of the Alexander Column, but not so long ago the issue was raised again. This time it was scientists who started talking about the safety of the monument.
For almost 190 years of its existence, the column has been restored six times: twice in the 19th century, three times in the 20th century, and 2002. The first obvious cracks were discovered in 1912. They were skillfully caulked up, but they continued to grow. At the last time, physicists and restorers examined the monument for three months: using ultrasound probing, calculated nuances on a mathematical model inspected every inch of the surface. A 29 mm slope from the vertical and about 57 cracks with a total length of 8 meters was registered.
“Having assessed the situation, the specialists concluded that the column will remain in a satisfactory condition for another 300 to 500 years. However, as geologists, we notice that a very important factor of the preservation of granite of the column itself was not taken into account. In the summer of 2021, our research team conducted a series of studies, and based on new information summarized: today we simply must return to the question of assessing the condition of the column. At the conference organized by the Museum of City Sculpture at the end of November, we drew specialists’ attention to an alarming fact which had been missed until then. Our statement interested many participants of the event. We are talking about the geological nature of fracturing, which is considered the main threat to the integrity of the monolith and may cause a revision of the previously voiced forecast. We are talking not only about obvious fractures but also about hidden, latent ones,” says Mining University professor Mikhail Ivanov, Doctor of Geological and Mineralogical Sciences.
Before it was extracted from the subsurface, the column was part of a granite massif characterized by several systems of different-age cracks. There are large horizontal ones, allowing huge chunks of rock to remain intact, combined with cracks of a different order of magnitude, higher. They are characteristic of the inner parts of the monoliths, which at first glance seem integral.
In geology, this phenomenon is known as “prototectonic separateness”. At a depth of 5-10 km, during the formation of a massif, the stress arising from cooling is deposited in it. Its magnitude may exceed the limits of rock elasticity and lead to the nucleation of latent disturbances in the structure at the intergranular level. These are not yet cracks, but, for example, loss of contact strength in the jointing between minerals. Such disturbances can be grouped into extended zones.
“This is the hidden from the eye reaction of the rock to the changed conditions of existence. In deep mines and workings, any geologist knows that if cracks are not visible, it does not mean that they do not exist. When such a rock is on the surface, the pressure decreases, and weathering factors, fluctuations in temperature and humidity are added, and the breaches open up. The cracks present in the Alexander Column are of the same nature. They are of the same type as the cracks observed in the granite massif, concentrated in three zones and oriented obliquely to the axis of the column. They were not seen when the monument was made. When it was lifted, turned over, the block stood for a certain number of years, they began to elongate and open. Each time they are plastered over, but it does not stop the process. When the block of granite was lying horizontally, the hidden cracks were in a state of compression. When the column was extracted and placed vertically, they went into a condition of expansion and were just doomed to open. Figuratively speaking, the geologists diagnosed, ‘The column is disabled!’ Since most of the cracks are grouped into extended zones oriented obliquely, the top of Alexandria tends to slide down one of them. We know the recipe for dealing with this affliction. If you ask any mining engineer what to do in a critical situation, he will answer - drill cross holes and tighten the blocks with anchors, which are effectively used for securing rocks in mine workings,” Mikhail Ivanov explained.
With high probability, we can say that in the future it will be specialists from the oldest technical school in the field of engineering geology, geophysics, and mining engineering who can assess the condition of the column from their knowledge and offer an acceptable solution to this problem to help experienced restorers.
This is not the only issue that links Mining University and the State Museum of Urban Sculpture. Currently, the planned restoration of the Bronze Horseman is underway for the upcoming anniversary - the 300th anniversary of the founding of the Russian Empire and adoption by Tsar Peter the Great of the title of the first Emperor of All Russia. The monument is completely shielded from the eyes of the townspeople by scaffolding. The employees of the university museum were asked to take part in the activities to ensure the safety of the granite pedestal.
According to Mikhail Ivanov, there is nothing critical, but the ongoing restoration work is really necessary and is not limited to cleaning and painting. Specialists are restoring the dilapidated fragments of the footing around the monument, and are taking care of the condition of the bronze. In particular, geologists have been involved to clarify the nature and role of the insert, which was found in the space between the three points of support. University students are now involved in geophysical research on the structure of the pedestal.
No less relevant and significant topic is the history of the Thunder-stone. At this point, there are quite a few legends about the original geography of the huge boulder, which later became the pedestal for the Bronze Horseman. For example, according to one version, it was dragged by the sea from Sweden, and according to another, its immediate homeland is the Olgino district near St. Petersburg.
The solution has been pondered over for years.
“The determination of the age of the Thunder-stone may allow us to advance in this matter. In modern conditions, it is done by the isotopic composition of such granite minerals as zircon. In the form of the smallest crystals, it is present mainly in the black mica, biotite. To apply this classical method to the centuries-old monument no one else had occurred to me before. No one but us. We have made a special tool that has been used this autumn to remove grains of biotite from the surface of the pedestal of the monument in many stages. It was true jewelry work! We gathered a teaspoon of this powder, processed it in a heavy liquid, and extracted several small zircon crystals. Then they were fixed and polished in a special preparation, which now allows us to take them to the Isotope Center of VSEGEI Institute, where we hope they will help us determine the geological age of zircon and, accordingly, the granite,” said the professor.
This may confirm the assumption of the scientific team of Mining University that the Thunder-stone is related to the rocks of the Vyborg massif of granite-rapakivi, which surface occur in the north of the Karelian Isthmus and Finland. Their age is estimated at 1.5 billion years. Thus, in the near future, the scientific community will be able to get an answer to the historical enigma.
