Stunning cliffs and caves are constantly evolving

Our zodiac tour boat ventured slowly into a cave, surfing on the powerful waves that have sculpted the stunning cliffs on Portugal’s southern coast, known as the Algarve. Just when I feared we’d crash into the jagged cave walls, the captain skillfully employed the engine to keep us away.

“I’ve never been to Arizona,” he said. “But people tell me this looks like Arizona.”

And indeed this cave does look like a cousin to the American southwest. The sandy stone layers come in a rainbow of yellow: gold, ochre, ginger, orange, rust, tan and terra cotta, with green and grey tinges thrown in for contrast over the teal waters.

We boated along the coast past caves, ledges, tunnels, bridges and sea pillars – independent columns that used to be attached to the cliffs. One little stack is called the Hedgehog, since it looks like that waddling animal in profile. When the sun hits the cliffs, they glow.

We passed several villages and towns. From the water, it’s clearer than from the land that humans have settled wherever a low point in the cliffs allows access to the sea via sandy beaches or even just a crack in the cliff.

Both erosion and people have changed this landscape.

Our friendly boat captain took us into cave after cave, giving us endless opportunities to take photos and crane our necks to take in the awe-inspiring creations of nature. However, there’s little information on how these spectacular landforms came to be. Once we got back to our apartment in the small town of Alvor, I did some research.

Millions of years ago, this land used to be under a shallow ocean. The rock was formed by layer upon layer of sand and silt and marine invertebrates – you can easily see whole shells in the rock. At some point, the land was “uplifted by tectonic activity or exposed by lowering sea levels, or both.” Erosion then began to expose the layers that we see today.

Pounding waves against the cliff base created and continues to create sea caves and ledges. From above, rainwater seeps into cracks and infiltrates the layers, forming and widening holes until they meet the caves below. As the erosion continues, chunks of the cliff fall off and sinkholes form.  

The caves are fascinating to explore, whether by boat or from the land. The next day, we drove to the town of Carvoeiro to walk along the boardwalk that hugs the cliff tops. At various points, wooden stairs led us downward to explore the network of rock formations. More stairs are carved out of the rock, with rope handrails to help with the uneven steps.

We ducked into caves and through arches – some natural and some man-made to allow access – and peered down wells and through notches in the rock. We stood above a blowhole and listened for the echoey thunder of the waves.

However, one main question of mine remained unanswered – are the cliffs made of sandstone or limestone or both?

Information panels along the boardwalk call it limestone, and indeed the top layer of stone does appear to be that greyish-white stone. But scientific websites that I perused refer to it as sandstone. Even my untrained eye can see that the layers look sandy and easily crumbled – especially when faced by the strong waves.

“Sedimentation was only resumed during Miocene times with bioclastic limestone that unconformable overlain the Mesozoic strata.” I admit I didn’t fully understand this website statement, but I took it to mean that there’s a layer of limestone over the sedimentary sandstone.  

People have been changing the landscape in the Algarve as well, ever since humans began settling here several millennia ago. The Romans, the Moors and the Portuguese have all left their marks on the landscape, including building along the coastline at water level and along the cliff tops. But the changes are proceeding faster than ever now.

One study has found that the cliffs are retreating faster due to human impact. “The areas of the coastline with human occupation are the worst affected by the effects of coastal erosion in Portugal, a situation that is set to get worse,” said a news article earlier this year.

We enjoyed exploring the rock formations, but I realized in retrospect that the tread of thousands and thousands of feet up and down the cliffs must speed the erosion. More and more building and development along the coast also contributes. And then there’s climate change. A recently reported study found that “vast areas of the Algarve will be underwater by 2050, irrespective of any action on climate change.”

It’s sad and ironic that these beautiful sedimentary layers laid down by the sea will eventually return to the water.