A LESSON PLAN ON THE GEOLOGY EXPERIMENT CARRIED OUT AT DAUGAVPILS SECONDARY SCHOOL NO. 3 IN LATVIA

KARST PROCESSES IN LATVIA

Introduction

Karst is a special type of landscape that is formed by the dissolution of soluble rocks, such as limestone, dolomite and gypsum. A karst process requires soluble, waterproof rocks and underground water. In addition, the water must be in motion, it must circulate in underground strata. It is characterized by underground drainage systems (such as karst aquifers) with deep sinkholes and even caves, which no one in Latvia has managed to access yet.

Chemical decomposition of the rocks occurs by dissolving and leaching the rocks because of groundwater and surface water. Groundwater serves as a development agent for the karst process and as it develops, geological risk increases, as well as the protection of groundwater from surface contaminants decreases. The carbonic acid that causes karstic features is formed as rain passes through Earth’s atmosphere picking up carbon dioxide (CO2), which dissolves in the water. Once the rain reaches the ground, it may pass through soil that can provide much more CO2 to form a weak carbonic acid solution, which dissolves calcium carbonate.

In Latvia karst processes are caused by infiltration of meteoric water, therefore it is most abundant in areas with no or thin Quaternary cover. In some areas surface features of karst processes such as sinkholes, karst shafts, land subsidence, lakes and dolines are present.

A sinkhole or doline is a depression or hole in the ground caused by some form of collapse of the surface layer. These sinkholes can be dramatic, because the surface land usually stays intact until the underground spaces just get too big. A sudden collapse of the land surface can occur if there is not enough support for the land above the spaces.

Karst processes in Latvia take place in rocks about 50 meters deep, making sinkholes in excess of even 10-meter depth. The karst process is slow. It takes dozens and hundreds of years. Therefore, it is almost impossible to forecast the development of this process.

Objectives: To observe the process of the formation of a sinkhole, a surface karst feature

                     To raise awareness about the processes underground and their impact on the earth transformation

Materials: a plastic box, a piece of paper, 200 ml sand, 2-3 tablespoons soda, 50 ml vinegar and a piece of chalk

Products: a sinkhole in the surface layer

Experimental procedure:

  1. Take a piece of paper and make a tube from it.
  2. Put the paper tube into a box.
  3. Fill the paper tube with soda (which substitutes limestone) and the box with sand.
  4. Put a piece of chalk near the paper tube.
  5. Pour vinegar on the soda in the paper tube and on the piece of chalk.
  6. Watch the formation of a sinkhole.
  7. Put the paper tube away and observe the collapse of the sand.

Expected results:

As you see, there is the chemical dissolution of carbonate rock (soda). The surface layer can stand for a short time, but if the sand collapses (because there is no longer support from the rock), a sinkhole forms.

Limestone (a piece of chalk) does not dissolves very quickly, as it takes a lot of time.