Seepage surfaces are places where groundwater slowly discharges to the ground surface without a clearly visible spring. Seepage surfaces reveal a great deal about how groundwater moves through the soil.
Seepage surfaces reveal groundwater movement
In nature, seepage surfaces may be a familiar sight to those spending time outdoors, but geologically they are interesting because they make the movement of groundwater visible.
Most groundwater is invisible to people, but at seepage surfaces, water that has traveled underground momentarily becomes a visible part of the landscape. They are small but important reminders that groundwater is a living part of an area’s geology and water balance.
What is seepage?
Term
Seepage (Finnish: tihkupinta)
Definition
An area where groundwater slowly seeps to the ground surface.
Explanation
A seepage area does not have a clearly visible discharge opening. Unlike a spring, the water emerges gradually over a broader area.
Source: Tieteen termipankki
Natural discharge points of groundwater
Groundwater does not only move deep underground — it is in constant connection with the surrounding landscape. Some rain and meltwater infiltrates the soil, travels through fractures in the ground and bedrock, and eventually discharges back to the surface. Such discharge points include springs, rivulets, and seepage surfaces. The discharge of groundwater is one natural part of the water cycle.
A seepage surface differs from an ordinary spring in that water does not rise from a single distinct point or pool. Instead, water seeps to the ground surface over a broader area. For this reason, a seepage surface may appear as, for example, persistently moist ground, a moss-covered zone, or a location where vegetation differs from its surroundings. At fen springs, groundwater may discharge in precisely this kind of seepage surface without any open water.
Seepage surfaces commonly form on slopes and terrain features where the groundwater table intersects the ground surface. This continuous moisture creates conditions for wetland vegetation and other spring-influenced species. Variations in soil composition and geological layers can also direct water upward or laterally toward the ground surface.
Seepage surfaces in Kurikka
Kurikka’s deep groundwater moves gradually downward from higher areas, such as the Lehtivuori region. Seepage surfaces occur along this route, and in Kurikka’s geology these surfaces are important because they reveal the pathways and discharge directions of deep groundwater.
Seepage surfaces are most visible in spring, when the ground has thawed and before vegetation covers them.