The Caldeirão on Corvo: the crater walk, the fog and what to bring

The Caldeirão is one of Corvo's main geosites. It is the collapsed summit of the island's volcano, and a road runs up to a viewpoint on its rim. The question is whether to look from the rim or to walk down inside. The loop inside is short and rated medium, but it is high, wet and often in cloud, and the weather at the top decides it more than your fitness does.

The Caldeirão is a collapse caldera at the top of Corvo's volcano, about 2.3 by 1.9 km across and roughly 305 metres deep, according to the Azores Geopark's geosite record. On its floor are two lakes, a wide wetland and a set of small scoria and spatter cones. Islanders say the lake and the cones make a map of the nine Azores islands; the official trail description repeats the story.

The rim rises to Morro dos Homens, 718 metres, the highest point on Corvo. The crater is part of the Azores Geopark, a UNESCO Global Geopark, and the whole island has been a UNESCO Biosphere Reserve since 2007. Thick peat moss covers the north-facing slopes inside and feeds the lakes, and the trail notes say the largest and oldest peatlands in Portugal are on Corvo and Flores.

From Vila do Corvo, the only village, the road climbs to the Caldeirão viewpoint. Local drivers wait at the harbour with minivans and take the ride in about ten minutes; ask to be collected later if you plan to walk. The geosite record lists the viewpoint as open at all hours with no entrance fee and parking for cars.

Walking up is possible but long: about 6 km and 550 metres of climb from the village, close to two hours. On a day trip it makes more sense to ride up and save your legs for the crater or the walk down.

The official trail round the crater is coded PRC02COR on the regional trail network. The numbers:

• Circular, 4.8 km, rated medium.
• About 2 hours 30 minutes.
• Between roughly 400 and 560 metres above sea level.

It starts near the Caldeirão viewpoint and goes down a track into the crater through vegetation dominated by sphagnum peat moss. At a very large boulder, the trail description tells you to take the right-hand track and go round the crater anticlockwise. On that stretch the waymark posts are shorter than usual, so that the cattle do not knock them over, and they are harder to see in low cloud. The path passes Poço da Velha and skirts a marshy area, comes back to the same boulder, and climbs back to the viewpoint.

Two warnings from the official description are worth reading before you set off:

• The lake level rises and falls through the year and can reach the level of the path. Where it does, take the drier line away from the banks rather than wading along the edge.
• Cattle, horses and goats graze inside the crater. Give them room and do not disturb them.

The Corvo municipality adds that some sections, especially in the Caldeirão, can be wet or slippery underfoot.

The second official trail on the island, PR01COR (Cara do Índio), links the Caldeirão with Vila do Corvo. It is linear, 10.3 km, medium and about three hours. From the crater it follows the road south, then dirt tracks past the Trevo stream and the island's water reservoirs. It goes round the Coroínha cone above the Pingas cliff and passes the basalt outcrop that islanders see as the face of an Indian. From there it drops between dry stone walls to the village, finishing at Praia da Areia near the windmills.

Combining the two gives a full walking day of about five and a half hours. That is realistic if you sleep on Corvo, or on a summer day trip when the public boat leaves you nearly seven hours on the island. It is too much for the five-hour window of the off-season boat.

The trail description says to walk the Caldeirão in good weather and visibility, and that advice sets the plan for the day. The municipality describes humid and foggy days as frequent on Corvo, especially at altitude. Annual rainfall is 1,000 to 1,500 mm, more on the high ground. On a bad day the cloud sits in the crater and you see nothing from the rim; one pair of day trippers had fog and rain at the viewpoint and a few minutes of clear view.

In practice:

• Check the rim before you commit. If the crater floor is invisible from the viewpoint, the loop is a walk through wet cloud with short waymarks, and the view is gone anyway.
• Keep the village as your fallback. If the top is in cloud, spend the morning below and ask the driver to take you up again later.
• Do not rely on the lakeshore for navigation. When the water is high the obvious line along the bank is under water, and the waymark posts are what you follow.
• Treat strong wind as a reason to stay off the rim. It is the most exposed place on the island.

The municipality's own list is short: suitable footwear, water, sun protection and a look at the forecast before you start. For the crater, that means:

• Boots or trail shoes with grip. The crater floor is peat and wetland, and the path is often wet.
• A waterproof jacket, even if Vila do Corvo is sunny when you leave.
• Water and food. Buy them in the village before you go up.
• A charged phone with the trail downloaded. The official trail pages offer GPS tracks.
• Cash for the van. Guides disagree on whether Corvo has a working cash machine, so bring euros from Flores.

How long does the Caldeirão walk take?

The official crater loop, PRC02COR, is 4.8 km and takes about two and a half hours. Allow extra time if the waymarks are hard to find in cloud.

Is the Caldeirão trail difficult?

It is rated medium. The distance and climb are modest, between about 400 and 560 metres of altitude, but the ground is often wet and slippery, and navigation gets harder in fog.

Can you swim in the Caldeirão lakes?

The official trail description tells walkers to keep away from the banks, because the lake level changes and can reach the path. The crater is a protected wetland; the place to swim on Corvo is Praia da Areia by the village.

What if the crater is in fog?

Wait or come back. Cloud on Corvo moves quickly, and a van ride back up later in the day is a better bet than walking a wet loop you cannot see.