Milhostovské mofety

Milhostovské mofety is a small but striking nature reserve tucked into the forest near the village of Ovesné Kladruby, in the Cheb district of the Karlovy Vary Region in the Czech Republic. Although its name references the neighboring hamlet of Milhostov, the site itself administratively belongs to the Ovesné Kladruby cadastral area, roughly 1.2 km south of Milhostov and 1.2 km east of the village of Vlkovice.

What are mofettes?

Mofettes are natural vents in the ground through which carbon dioxide of volcanic origin escapes from deep within the earth's crust. At Milhostovské mofety, these take the form of small craters, some tens of centimeters deep. Up to fifteen such vents can be counted across the site, varying in size and in how actively they release gas.

What the site looks like

Most of the mofettes stay dry for much of the year, with the gas simply seeping out of the dry crater floor — sometimes visible only as faint bubbling or a distinctive smell. A handful of the deeper craters, however, hold standing water that is strongly acidic, with a pH around 2.2, and rich in dissolved carbon dioxide. That chemistry is what gives the place its faintly otherworldly, miniature-volcano feel, even though the region has had no active volcanism for a very long time.

Where the gas comes from

The mofettes owe their existence to the geological history of the Cheb Basin, a region known for ongoing seismic activity and traces of past volcanism — the same geological setting that produces the mineral springs of the nearby spa towns of Mariánské Lázně and Františkovy Lázně. Carbon dioxide generated deep underground rises through cracks in the rock and escapes at the surface, creating these small, gently bubbling spots in the forest floor.

A word of caution

Visitors should be careful: the escaping carbon dioxide is heavier than air and can accumulate close to the ground and in low-lying hollows, occasionally reaching concentrations that pose a health risk under certain weather conditions. It's best to avoid lingering bent over directly above a crater for long periods, and small children or pets should not be allowed to approach the deeper hollows unsupervised.

Frequently asked questions

How do you get to Milhostovské mofety? The easiest starting points are the villages of Ovesné Kladruby or Milhostov, from which forest paths lead directly to the reserve, which sits in woodland away from any main roads.

Can the gas actually be dangerous? Yes, in principle — under unfavorable weather conditions, carbon dioxide concentrations near the ground can become harmful, so it's wise to avoid spending long stretches of time right next to the craters, especially on still, windless days.

How many mofettes are there? Up to fifteen have been counted, differing in size and activity — some are dry, others filled with strongly acidic water.

Is this a volcanic area? The Cheb Basin has a long history of seismic and volcanic activity, and the mofettes are one of the visible traces of those processes, even though there is no active volcano at the site itself.