Mravenčák

Mravenčák is a small but geologically remarkable volcanic hill just south of Klášterec nad Ohří, on the right bank of the Ohře River in the Chomutov district. It rises to 531 metres above sea level and forms part of the northern Doupov Mountains (Doupovské hory).

Where does this hill come from?

Mravenčák is the remnant of a Tertiary-period volcano. It formed through a Strombolian-type eruption, in which the volcano first ejected volcanic bombs and ash, followed by a later phase of lava flows. This activity shaped the hill's distinctive conical form, which today is mostly wooded but still shows exposed rocky outcrops near the summit — visible evidence of its volcanic origin.

Why is the hill protected?

In 1990, the summit area of Mravenčák — covering 1.5 hectares — was designated a natural monument. The protection targets the rocky, sun-exposed summit, home to a warmth-loving steppe plant community that is uncommon in this part of the Czech Republic. This combination of volcanic geology and specialised flora makes Mravenčák a spot of interest not only for hikers but also for botanists and geologists.

How do you get to Mravenčák?

A forest path runs along the hill's southern and western slopes, and a red-marked hiking trail from Klášterec nad Ohří leads across Mravenčák itself. From there, the trail continues to the ruins of Egerberk Castle and then over the Úhošť hill all the way to Kadaň. It's a convenient route for combining a walk up the hill with a visit to nearby historical ruins — the whole loop can easily be planned as a half-day hike.

What will you see along the way?

Along the trail you'll notice clear rocky outcrops that reveal the hill's volcanic structure, while the summit itself hosts the protected steppe vegetation — quite different from the forest that surrounds it in the rest of the Doupov Mountains. It's a good place to see, in a small area, how ancient volcanic activity shaped this part of the Czech landscape, and how a warmth-loving plant microhabitat survives within a wooded hill.

When is the best time to visit?

Spring and early summer are the best times to come, when the steppe vegetation on the summit is in full bloom. The trail is accessible year-round, but the ground near the top can be rocky and uneven, so sturdy hiking footwear is recommended regardless of season.

Frequently asked questions

What is Mravenčák? It's a 531-metre volcanic hill on the right bank of the Ohře River, south of Klášterec nad Ohří, formed as the remnant of a Tertiary Strombolian-type volcano.

Why was Mravenčák made a natural monument? Since 1990, its rocky summit (1.5 ha) has been protected for its rare, warmth-loving steppe vegetation.

How do you reach Mravenčák from Klášterec nad Ohří? Follow the red-marked hiking trail, which continues on to the ruins of Egerberk Castle and then via Úhošť to Kadaň.

Can you still see traces of the volcanic past on the summit? Yes — exposed rocky outcrops near the top reveal the structure of the former volcanic cone, built up from ejected bombs, ash, and later lava flows.