Dagnija Pāruma is a 2nd year geology student at the Faculty of Geography and Earth Sciences of the University of Latvia. At the end of the spring semester in 2008 she completed a term paper on the geological past of Andrejsala, supervised by geography professor Laimdota Kalniņa. Besides, Dagnija is a professional full-time geologist employed by SIA Ģeo for about two years, which has helped her to put her theoretical knowledge in use in practical hands-on contexts.

While working on the paper, Dagnija researched Andrejsala's geological profile, development over time and sediment accrued here during the various ages of the Baltic Sea. "I chose Andrejsala as the subject matter because I knew about its future development plans, including new construction. It felt like participating in the development of Rīga. I also wanted my paper to differ from many other students' research projects, as those usually consider certain exposed geological features, fossils, sediments in swamp lakes and their build-up. My intention was to come up with more comprehensive findings, not just providing some information about the geological engineering parameters of Andrejsala's soil but also revealing the origins of the [former] island," Pāruma explains. She was able to obtain the necessary source data, such as the topographical map, geological cross-sections and analyses of sediment samples at SIA Ģeo, because her company had been entrusted with a geological survey and probing work of Andrejsala in the autumn of 2007.

It took about 3 months to gradually develop the term paper, and during that period Dagnija perused and thoroughly analysed a range of books and maps. She also participated in fieldwork, learned the details of pinpointing the types of soil obtained by probing, practiced laboratory work, carried out some granulometric analysis of sediments as well as used a specialised software application to process experimental data and obtain a geological cross-section of the site.

The research data shows that Andrejsala and a number of other north Rīga's areas geologically have appeared under circumstances that combine several interacting factors, resulting in the current tectonic shapes of the Latvian capital. During the Quaternary Period, sharp changes affected the region, including several ice ages and interglacial periods. It is alleged that in the most recent interglacial stage the north part of Rīga was part of sea bottom. When glaciers crept in, they did to a certain extent change the bedrock relief; when they retreated, the base part of the quaternary sediments was formed. The paleogeology also tells us that even in the latter transformations—a mere 12,000 years ago—the changes of the soil were rather drastic.

After the latest known ice age, a proglacial lake appeared, which about 11,500 years ago turned into a part of the Baltic Ice Lake, and after another 500 years the territory was covered by the waters of the Yoldia Sea. During the Littorina Sea's period of transgression (some 8,000 years ago), when the sea level was 7 to 14 metres higher than it is now, most of the nowadays Rīga's territory was undersea. At the same period, the area accumulated sludge, including Andrejsala, where two thick layers of sludge have been discovered, both formed during the Littorina Sea stage.

The current coastal area and its relief features appeared during the Post-Littorina Sea stage. The latter sea began its existence about 4,500 years ago, yet post-littorine sediments have not been found in Andrejsala since the historic sea's water level was similar to that of today's Baltic Sea.

Pāruma also writes that Andrejsala's geologic becoming was closely related to the appearance of the river Daugava. In 1972 professor Guntis Eberhards, who also advised Pāruma during her term paper work, had already pointed out that Andrejsala, as well as three other islands, Doles sala, Mārtiņsala and Zirņu sala, were created during the regression of the Baltic Ice Lake approximately 10,000 years ago—the Daugava then forked, while bursting into a plain. Eventually, the modern shape of the riverbanks appeared as late as at the beginning of the 20th century, while the Daugava's branch separating the island from the current area of Eksporta Street was artificially filled up.

Dagnija Pāruma's plans for her next study year include a BA paper. The young specialist admits that she might continue to research Andrejsala: "It could be interesting to determine the maximum bearable loads of the sand and sludge layers of Andrejsala's soil."

Pāruma's paper (in Latvian), titled Andrejsala's Geological History, can be seen at the office of Jaunrīgas attīstības uzņēmums (address: Andrejostas Street 4a, Rīga; please book your visit by e-mail).

Related material is available in our website's History section.