La Palma's geography is a result of the volcanic building of the island. The highest peaks reach about 2.4 km above sea level, and the foundation of the island reaches more than 3 km below sea level. The northern part of La Palma is dominated by the Caldera de Taburiente, the largest erosion crater in the world, with a width of 9 km and a depth of 1.5 m. It is surrounded by the Cumbre Vieja, a ring of mountains ranging from 1.6 km to 2.4 km in height. Only the deep canyon Barranco de las Angustias leads into inner area of the caldera which is a national park. It can be reached only by hiking. The outer slopes are cut by numerous gorges which run from 2 km down to the sea. Today, only few of these carry water due to the water tunnels.

Through the southern part of La Palma leads the ridge Cumbre Nueva formed by numerous volcanic cones built of ashes, providing a rather bizarre landscape. The southern cape Punta de Fuencaliente, where the most recent volcanic activities took place, consists of lava and ashes.

La Palma is dominated by the colors blue, green and black. Blue is the surrounding ubiquitous sea. Green comes from the abundant plant life which is the most diverse in the Canary Islands. Black comes from the volcanic rocks that still fill the landscape, and from the numerous small beaches made of black sand.

The island was formed as a seamount by the volcanic activities like all of the Canary Islands. La Palma is the most active volcano of the Canary Islands and was formed 3 million years ago. It rises 3.5 km from the seafloor to the sea surface and reaches a height of 2.426 km above sea level. 500,000 years ago the primary volcano Taburiente collapsed with a giant landslide which formed the Caldera de Taburiente. The known historic eruptions are:

• 1470-1492 Montaña Quemada
• 1585 Tajuya near El Paso
• 1646 Volcán San Martin
• 1677 Volcán San Antonio
• 1712 El Charco
• 1949 Volcán San Juan, Duraznero, Hoyo Negro
• 1971 Volcán Teneguía

During the 1949 eruption the western half of the Cumbre Vieja ridge slipped several metres downwards into the Atlantic Ocean. It is believed that this process was driven by the pressure caused by the rising magma heating and vaporizing water trapped within the structure of the island. During a future eruption, the western half of the island, weighing perhaps 500 billion tonnes, could slide into the ocean. This could generate a giant wave known as a megatsunami around 1 km high in the region of the islands. The wave would fan out across the Atlantic and strike the Caribbean and the eastern American seaboard several hours later with a wave possibly 90 m high causing massive devastation along the coastlines. However, some scientists think the flank of the island would crumble away, instead of falling into the ocean in a large mass, sparing the coasts.