South Iceland's Dynamic Geosites: Geysers, Glaciers, Rifts, and Rumbling Volcanoes

South Iceland is a dramatic landscape where nature's forces collide spectacularly across 300 km of territory that spans two diverging continents. This region, renowned for its volatile beauty, hosts some of Iceland's most infamous volcanoes and glaciers, nestled above vast expanses of black sands composed entirely of volcanic ash. These sands are products of fiery eruptions beneath ice caps, phenomena so unique to Iceland that the term "jökulhlaup" (glacial outburst flood) is recognized globally among geologists. South Iceland offers an unparalleled glimpse into the dynamic processes that sculpt and define this fierce region.

At the heart of this region lies Katla UNESCO Geopark, named after the infamous Katla volcano. This geopark spans three municipalities and showcases a diverse range of geological features, including volcanic craters, lava fields, and glacial landscapes. It serves as a living laboratory for understanding the powerful interactions between volcanic activity and glacial dynamics.

South Iceland includes The Golden Circle route, a popular tourist trail, takes visitors to some of Iceland's most famous geological sites, including Þingvellir National Park, Geysir geothermal area, and Gullfoss waterfall. Going further east, the South Coast route offers stunning coastal views, black sand beaches, and iconic landmarks such as Eyjafjallajökull volcano that spewed ash over Europe in 2010, Dyrhólaey and Reynisfjara. South Iceland is also home to Vatnajökull National Park, one of Europe’s largest protected areas, which includes the immense Vatnajökull glacier and a variety of volcanic landscapes.

Not to be missed are the Westman Islands archipelago off the south coast. This includes Heimaey Island, known as the "Pompeii of the North," where a 1973 eruption buried the town, which has since been rebuilt. The archipelago also features the UNESCO World Heritage Site Surtsey, a volcanic island formed in 1963. Surtsey remains a pristine natural laboratory for studying ecological succession and is closed to public access. However, Heimaey Island is easily accessible by an electric ferry, which takes about 20 minutes from Landeyjahöfn harbor on the South Coast. For those visiting the Westman Islands, the award-winning Eldheimar Museum is a must-see. It showcases the 1973 eruption events and serves as the visitor center for Surtsey Island.

Below we have selected five geosites that showcase the primary geological phenomena found in South Iceland. However, like the rest of the country, the entire region offers endless discoveries and rewards for enthusiastic geology explorers.

Þingvellir is a unique site both geologically and historically, showcasing clear manifestations of diverging tectonic plates.

1. Þingvellir: Bridging Continents and Cultures

Location: Þingvellir is part of the Golden Circle route, located in the southwestern part of Iceland, about 45 kilometers northeast of Reykjavik via Route 36 (Þingvallavegur) that connects with Ring Road no. 1. See on a map.

Þingvellir is a National Park and a UNESCO World Heritage site and is famed for its historical, cultural, and geological significance. It is one of the few places on Earth where you can see the manifestations of the North American and Eurasian tectonic plates pulling apart.

Geologically, Þingvellir is exceptional because it lies directly on the Mid-Atlantic Ridge, where the Eurasian and North American tectonic plates are pulling apart. This rift is evident in the dramatic cliffs and fissures that scar the landscape, visible signs of the Earth’s crust stretching and splitting. The largest rift, known as Almannagjá, serves as a stark reminder of the ongoing dynamic geological processes. 

Actually, it's not entirely accurate to say that this area lies directly on the boundary of the major tectonic plates because there are indications of a microplate, known as the Hreppar Microplate, located between them. However, this does not change the overall picture, and the existence of the microplate is part of the boundary dynamics of the major plates.

The rift valley itself stretches over about 10 km and also encompasses Þingvallavatn, the largest natural lake in Iceland. This lake is fed by underwater springs originating from the Langjökull glacier inland, creating a unique ecosystem within its waters.

Hydrologically, Þingvellir is significant due to its underground rivers flowing through porous lava fields, emerging in springs throughout the park. This interaction of groundwater with volcanic rock filters the water, making it exceptionally clear and pure. Fissures, in the rift valley are filled with this clear water, famed for its visibility and the Silfra fissure is a popular diving spot, offering a literal dive between continents.

The rift valley at Þingvellir is a stunning example of continental drift that forms through a series of geological processes:

1. Tectonic Activity: Þingvellir is located on the Mid-Atlantic Ridge, where the Eurasian and North American tectonic plates are gradually diverging. This tectonic movement is fundamental to the formation of the rift valley.
2. Rifting: As the plates pull apart, tension forces the Earth's crust to stretch and thin. Over time, this stress causes the crust to crack and form faults - and cause earthquakes.
3. Formation of a Graben: The area between faults drops down to form a graben, or sunken block, creating the characteristic rift valley seen at Þingvellir. The valley is flanked by higher blocks of crust, known as horsts.
4. Volcanic Activity: Magma forms due to decompression processes and rises through the thinning crust, occasionally erupting as lava, and eventually filling the rift valley.
5. Ongoing Process: The rifting at Þingvellir is an ongoing process, with the valley continuously forming as the tectonic plates diverge at a rate of about 2 cm per year, visibly altering the landscape over time.

Much like rainbows and the northern lights, watching Strokkur erupt every few minutes is a natural phenomenon one can never tire of.

2. Geysir Geothermal Area: Witnessing the Intermittent Majesty of Strokkur and the Historic Great Geysir

Location: Geysir is situated in the Haukadalur Valley in southwestern Iceland, approximately 110 kilometers east of Reykjavik. Geysir is part of the Golden Circle route. See on a map.

Safety is paramount in this location: it is crucial to stick to marked paths and avoid direct contact with the boiling waters of the hot springs. Also, stay on the wind side of Strokkur geyser!

The Geysir Geothermal Area stands as one of the island's most iconic tourist attractions. Despite the diminished activity of the Great Geysir, which historically erupted every few hours until ceasing in 1916, the field remains a geothermal spectacle.  The lively Strokkur geyser, spectacularly erupts every few minutes sending jets of boiling water up to 30 meters high, this area embodies the powerful forces beneath the Earth's crust. 

The Geysir Geothermal Area truly lives up to its reputation. Spouting geysers are a rare phenomenon, mainly found in Geystir Iceland, Yellowstone USA, New Zealand, Japan and on Kamtchaca. And witnessing one erupt so regularly and intimately as is possible here, is an extraordinary experience. Visitors to this steaming terrain are treated to more than visual wonders; they feel the earth tremble and hear the eruptions' roar, making their visit both awe-inspiring and immersive. Those who don't pay attention to the wind direction might also get an up-close introduction to the water as the spray falls back to earth.

The term "geyser" itself, derived from the Icelandic "geysir" meaning "gusher," points to the influence of the Great Geysir. Documented accounts trace its active periods back to the late 13th century, likely spurred into existence by seismic activities and volcanic eruptions from nearby Mt. Hekla. Although its eruptions have waned, the Great Geysir has left a lasting name for such phenomena worldwide.

Today, Strokkur holds the mantle as the primary attraction, captivating tourists with its regular and reliable displays. The entire area lies over a vast geothermal field, signaling the immense heat that fuels these natural spectacles from below.

How geysers form
The Geysir geothermal area in Iceland was primarily shaped by local volcanic heat and geological structures. Here, there is a steady inflow of groundwater, originated from the Langjökull glacier. The groundwater is heated by a magma intrusions at this very small and extinct Geysir central volcano. As the water heats up, it dissolves minerals from the host rock and becomes pressurized due to being confined within rock formations and mineral cap. When the pressure builds enough to break through to the surface, it can lead to the dramatic eruption of geysers or the gentle flow of hot springs, depending on the conditions of the escape route.

Additionally, seismic activities periodically alter these underground pathways, directly influencing geyser behavior by opening new channels or closing existing ones. These changes can trigger periods of increased or decreased activity in the geysers, making the area a dynamic and ever-changing landscape. The cooling of this mineral-rich water at the surface creates intricate deposits around the vents, contributing to the unique and rugged terrain of the Geysir area.

How geysers work

Understanding how a geyser works enriches the visitor experience, it has everything to do with thermodynamics of water and it’s boiling point at different pressures: 

1. Water Seepage: Rainwater and snowmelt seep deep into the earth through cracks and porous rock, filling underground reservoirs or cavities.
2. Heating: This water comes into contact with heated rocks from magma intrutions beneath the surface. Because of the intense heat from the earth’s interior, the water temperature rises, eventually reaching beyond its typical boiling point. The water remains liquid due to the high pressure from the surrounding rock.
3. Steam Formation: As the water continues to heat, some of it begins to convert into steam. However, because it is under pressure, the steam does not immediately escape.
4. Pressure Buildup: The steam accumulates, increasing pressure in the underground chamber. This pressure pushes the superheated water and steam upwards through any available fractures or openings.
5. Eruption: When the steam and hot water find a path to the surface, the pressure is suddenly released. This decrease in pressure allows the boiling point of the water to drop, causing the water to rapidly convert into steam. The water expands approximately 1,700 times its original volume, which forces more water to vaporize and drives a powerful column of hot water and steam out of the geyser’s vent, resulting in a dramatic eruption.

Recovery: After the eruption, water starts refilling the chamber, and the whole process begins again.

The Dyrhólaey Headland boasts Iceland's grandest coastal arch and offers splendid views of black sand beaches, infamous volcanoes, and even burrowing puffins during the nesting season.

3. Dyrhólaey: Iceland’s Grand Coastal Arch

Location: Dyrhólaey headland is located on the southern coast of Iceland, near the town of Vík í Mýrdalur, approximately 180 kilometers southeast of Reykjavik. It is part of the South Coast Route. The main parking location is on the lower part of the island (see on a map). To get to the top you can either hike or drive a rather steep gravel road (not passable for all cars and closed during winter).

! Show extra caution near the edges of Dyrhólaey, as they can be very unstable and are filled with puffin burrows.

Dyrhólaey, a prominent headland on Iceland’s southern coast, is renowned for its striking natural beauty, abundant birdlife, and magnificent views. Originally an island formed by a volcanic eruption during the Late Pleistocene (the last Ice Age), Dyrhólaey now connects to the mainland. Rising 120 meters above sea level, it offers stunning vistas of the Mýrdalsjökull glacier, covering Katla volcano, to the north, Eyjafjallajökull to the northwest, and the extensive black sand beaches of Reynisfjara to the east and Dyrhólasandur to the west.

Geologically, Dyrhólaey is a marvel. This headland, originally formed as a submarine volcanic island, is primarily composed of well-bedded tuff resulting from hydromagmatic explosions. These explosive interactions between lava and seawater create a unique type of igneous rock known as hyaloclastite, which is particularly common in Iceland due to its dynamic volcanic activity and interaction with ice and water. On the eastern flank of Dyrhólaey, the tuff sequence is capped by compound pahoehoe lava, exhibiting cube jointing caused by water-enhanced cooling. This sequence is typical for Surtsyean eruptions, indicating that the volcano once extended further out into the sea before erosion took its toll.

Dyrhólaey, whose name translates to "door hill island," aptly describes the massive arch-shaped rock formation that extends into the North Atlantic Ocean. This natural arch is large enough for small boats to navigate through. It stands as one of Dyrhólaey's most iconic features, a testament to the powerful erosive forces of wind and waves continually reshaping the coastline. The headland also boasts several sea stacks, remnants of ancient volcanic activity, which add to the dramatic and picturesque landscape. The erosion process is ongoing, with significant rock falls recorded, such as in 2012 when a large section of the cliff fell into the sea.

Dyrhólaey's volcanic origins are further highlighted by its division into two parts: Háey (High Island) and Lágey (Low Island). A local geologist Einar Einarsson has extensively studied the formation and geology of Dyrhólaey, describing the headland’s evolution through multiple eruptions. His research indicates that the first eruption formed the eastern end, now called Skorpunef, while the second eruption shaped the majority of the current landmass.

The area around Dyrhólaey is rich in geological features. The headland was shaped significantly by glacial and oceanic forces over thousands of years. Notably, the 1918 Katla eruption deposited a vast amount of sediment southwards, forming Kötlutangi, which now extends further south than Dyrhólaey, making it Iceland’s southernmost point.

Dyrhólaey is not just a geological wonder but also a sanctuary for birdlife. Declared a protected area in 1978, it is a crucial breeding site for seabirds like puffins, kittiwakes, and arctic terns. During the breeding season, access to parts of the headland is restricted to protect these nesting birds.

The vast, moss-covered Eldhraun lava field, created by one of the largest eruptions in history, is a must-stop on the route between Vík and Kirkjubæjarklaustur.

4. Eldhraun Lava Field: A Testament to Iceland's Volcanic Fury

Location: The Eldhraun Lava Field is situated in the southern part of Iceland, between the towns of Vík í Mýrdal and Kirkjubæjarklaustur. It is about 234 kilometers southeast of Reykjavik. The main parking area offers a short hiking path and information signs. See location on a map.

The Skaftáreldahraun lava field, also known locally as Eldhraun, is one of Iceland's most significant geological features. It was formed during the catastrophic Skaftá fires (Skaftáreldar) of 1783-1784. This event is one of the largest volcanic eruptions in recorded history and had profound local and global impacts.

The Laki eruption was a series of fissure eruptions along a 27-kilometer-long volcanic fissure in the Grímsvötn volcanic system. Over eight months, the eruption produced an estimated 14 cubic kilometers of basalt lava, covering approximately 565 square kilometers of land. The resulting lava field, Skaftáreldahraun, is a testament to the sheer volume of volcanic material expelled during this period. The Laki crater row area is in the highland of Vatnajökull National Park and accessible via 4x4 F-road during the summer.

The lava field is primarily made up of basaltic pahoehoe lava, characterized by its smooth, billowy, or rope-like surface. This type of lava is highly fluid and can flow over long distances, creating extensive, relatively flat lava fields. The smooth surfaces and unique formations within Skaftáreldahraun provide a striking contrast to the rugged Icelandic landscape.

The ecological succession of Skaftáreldahraun is equally impressive. Over the centuries, the harsh and barren lava field has gradually been colonized by mosses and lichens, creating a green blanket that softens the stark black lava. This moss layer plays a crucial role in the ecosystem development, retaining moisture and providing a habitat for various plant species, insects, and small animals. This transformation from a fiery wasteland to a lush, green landscape illustrates nature's resilience and ability to heal over time.

The historical and cultural significance of the Skaftáreldahraun lava field adds another layer of interest. The Laki eruption had devastating effects on Iceland, causing widespread crop failures, livestock deaths, and leading to a severe famine that killed about a quarter of the island's population. The ash and sulfur dioxide released into the atmosphere created a volcanic winter, lowering global temperatures and affecting weather patterns worldwide. This event is deeply etched in Icelandic history and has been the subject of numerous studies in volcanology and climatology.

For visitors, Skaftáreldahraun offers a unique opportunity to witness the aftermath of one of the most powerful natural events in human history. Walking paths and trails wind through the lava field, allowing for an up-close exploration of the distinctive pahoehoe formations and the verdant moss that now covers much of the area. The landscape's stark beauty and the sense of walking on a geological feature of such historical importance make Skaftáreldahraun a must-visit destination for geology enthusiasts and nature lovers alike.

The lava field is also a gateway to understanding the broader volcanic activity in the region. It is part of the larger volcanic system that includes the Grímsvötn and Katla volcanoes, both of which remain active.

The icebergs in the glacial lakes at the snouts of Vatnajökull's outlet glaciers often contain layers of volcanic ash. This ash is from nearby volcanoes like Öræfajökull, which devastated the area with a catastrophic eruption in 1362.

5. Jökulsárlón Glacial Lagoon: Where Fire Meets Ice

Location: Jökulsárlón Glacier Lagoon is situated in the southeastern part of Iceland, within the southern region of Vatnajökull National Park, along Ring Road No. 1.

Jökulsárlón Glacial Lagoon is one of Iceland's most spectacular geosites, renowned worldwide for its breathtaking beauty and unique geological significance. Located in the Southern region of Vatnajökull National Park in southeast Iceland it sits at the base of Breiðamerkurjökull, an outlet glacier of the mighty Vatnajökull ice cap. Crowning the lagoon is the Öræfajökull volcano, which features Iceland's highest peak at 2,110 meters. The surrounding area, named Öræfi or "the wasteland," was so called after a catastrophic eruption in 1362 that devastated the once fertile farmland with pyroclastic flows and glacial floods.

Jökulsárlón is a relatively recent natural phenomenon, having formed around 80 years ago as the Breiðamerkurjökull glacier began to retreat. At that time, the glacier extended much further across the coastal plain than it does now. The thinning and retreat of the Vatnajökull ice cap, driven by climatic changes, have drastically altered the landscape, creating the expansive lagoon we see today. Vatnajökull, the largest ice cap in Europe, is retreating at an alarming rate, significantly impacting its outlet glaciers.

Breiðamerkurjökull is one of the largest outlet glaciers flowing southwards from Vatnajökull and the largest one east of Öræfajökull. This glacier, which flows at a rate of about 500 meters per year, originates from the high mountain range of Esjufjöll. The glacier's snout lies in a deep basin, forming the deepest lake in Iceland at 268 meters. The river Jökulsá á Breiðamerkursandi flows from Jökulsárlón, making it the shortest yet one of the most immense glacial rivers in the country.

The retreat of Breiðamerkurjökull and other outlet glaciers has significant implications for the surrounding landscape. As the glaciers recede, they leave behind depressions that fill with meltwater, forming glacial lakes like Jökulsárlón. The continuous melting and calving of icebergs into the lagoon create a dynamic and ever-changing landscape.These icebergs, with their striking blue and white hues, float across the lagoon before melting or being carried out to sea. Many icebergs also feature noticeable black stripes, which are layers of volcanic ash deposited during eruptions of the mighty volcanoes beneath the ice cap. These include some of Iceland's largest and most active volcanoes, such as Bárðarbunga and Grímsvötn. Eruptions beneath the ice produce ash when the intense heat from the volcanic activity melts the ice, causing explosive interactions between magma and water. This interaction fragments the magma into fine ash particles, which then settle onto the glacier and become embedded in the ice over time.

The coastal plain in front of Breiðamerkurjökull, known as Breiðamerkursandur, has been shaped by both glacial and volcanic processes. This plain, formed by glacial outburst floods (jökulhlaups) associated with subglacial eruptions and fluvial action, is now undergoing significant changes due to coastal erosion. As the glacier's flow of sediment has diminished, the coastline is retreating. This poses a threat to infrastructure, including the Ring Road No. 1 and the bridge over the river Jökulsá, which may be endangered if the land between the lagoon and the sea continues to erode.

Visitors to Jökulsárlón can explore the lagoon by boat, getting an up-close view of the icebergs and the occasional seals that inhabit the waters. The nearby Diamond Beach, where icebergs wash ashore and glisten on the black sand, provides a stark and beautiful contrast to the icy lagoon.