How does a church built from stones survive 70 years under water?

Question

Following the recent news about the Sau reservoir in Spain, the draught revealed an 11-century stone church which has been under water for 70 years since 1962 when the reservoir was built.

How is it technically possible, that the stone building survived 70 years under water without serious structural damage and has not collapsed? Why didn't the mortar gluing the stones dissolve throughout the years and the movement of the water did not disassemble the building?

Before:

Now:

See more picture of the church here.

Answer 1

See the rubble around it? that's other buildings that were less robustly put together that fell apart. And you can see the first floor of another tower that did collapse.

Older building techniques don't rely on the mortar holding the structure together, instead it's the interlocking bricks and structure of the arches holding each other up.

That reservoir would have been fairly still water, so there is no movement of water to push it around.

Answer 2

The first part of the answer should be that basically neither stone nor mortar are soluble in water, so stone, mortar or concrete structures can last for quite long in water even if they weren't conceived to be underwater. In fact, there are a lot of stone or concrete structures conceived to be underwater that are fine after decades or centuries - for example, bridge pillars and foundations, dams or piers.

The second part of the answer is that Sant Romà de Sau church has been actively maintained since it was first covered by water in 1962. For example, this article from 2012 mentions that restoration works had been carried 15 years before (that is, about 1997). Sant Romà de Sau is a cultural and touristic landmark and is cared for as such. Without that maintenance the church would be in worse condition nowadays. The remaining of the village doesn't benefit from such an status, in addition to be less water resistant.

Answer 3

As Pere mentioned stone structures can last a long time underwater. There are many buildings around the world that appear during drought conditions. Here are some pictures of the Temple of Quichula, a 16th century Catholic Church.
The Temple of Quechula was built in 1564 and abandoned in 1776. It was submerged in 1966 after a dam was built and occasionally reappears. It’s still pretty structurally intact.
This one hasn’t had any maintenance, and was already a ruin when submerged.

What surprises me about the Sant Romà de Sau church is the roof. It must be supported by wooden beams and that still looks solid.