Key takeaways
- Descend into drilled shafts where ground temperatures reach 100°C just metres below the surface, a legacy of volcanic activity centuries past.
- Watch water poured into a borehole instantly erupt as steam, demonstrating the extreme heat trapped in the rock beneath your feet.
- See dried vegetation ignite spontaneously when placed over a vent, revealing how the geothermal energy can combust fuel without a spark.
- Observe food cooking over an open lava pit using only the natural heat from below, a working demonstration of volcanic energy harnessed for cooking.
- Learn why Islote de Hilario has remained geothermally active for 300 years and what makes standing above these vents a safe visitor experience.
The Theatre of Heat at Islote de Hilario
At the heart of Timanfaya National Park stands Islote de Hilario, a volcanic plateau where the Earth's raw power becomes visible and tangible. This is where three distinct geothermal demonstrations unfold in sequence, each one revealing a different aspect of the intense heat trapped beneath the surface. Visitors gather at viewing platforms to witness geyser eruptions, brushwood fires igniting spontaneously, and food cooking directly over a lava pit at the El Diablo grill. Together, these demonstrations tell the story of how volcanic heat persists three centuries after the eruptions that shaped this landscape.
The site takes its name from Hilario, a hermit who lived in isolation on the plateau during the 18th century and whose presence became intertwined with the volcanic phenomena. Today, thousands of visitors each year come to experience what Hilario would have witnessed: the theatre of geothermal energy in its most dramatic form. Each demonstration is not merely spectacle but a window into the physics of volcanic systems and the remarkable stability of subsurface heat over geological timescales.
The Geyser: Water Meets Superheated Rock
The first demonstration involves pouring water into a narrow borehole that descends several metres into the ground. Within seconds, the water encounters rock so hot that it flashes instantly into steam, erupting from the hole with force and a distinctive roar. This happens not because magma lies just below, but because the rock itself has been heated to temperatures exceeding 200 degrees Celsius. The water does not need to reach boiling point in the traditional sense; the intense pressure at depth and the extreme temperature of the stone cause a violent phase change from liquid to gas.
This geyser effect demonstrates a fundamental principle of thermodynamics. The ground at Timanfaya retains heat far beyond what surface conditions would suggest. Water introduced to such temperatures vaporises so rapidly that the steam expands with enough energy to propel water droplets and vapour upward in a plume. Visitors witness the result within a few seconds of the water being poured, making this one of the most immediate and visceral examples of geothermal power available anywhere.
Steam erupts from the volcanic borehole at Islote de Hilario
The Brushwood Fire: Spontaneous Ignition from Below
In the second demonstration, dry brushwood is placed over another opening in the ground, and within moments it ignites without any visible flame or spark applied from above. The wood does not burn gradually; it catches fire from the radiant heat rising through the opening, flames appearing as though the ground itself is burning. The temperature required to achieve this spontaneous ignition is typically around 300 degrees Celsius or higher, showing that the heat at depth exceeds even the most extreme surface conditions in this arid landscape.
This demonstration vividly illustrates the gradient of temperature that exists beneath Islote de Hilario. Just a few metres down, the rock is hot enough to ignite dry wood instantly. The hermit Hilario, who would have observed such phenomena during his years of solitude, may well have used this natural heat source for warmth and cooking, adapting to an environment where the volcano itself provided energy.
The El Diablo Grill: Cooking Over a Lava Pit
The third and perhaps most practical demonstration is the El Diablo grill, a simple metal grid placed over another opening to the hot rock below. Meat, fish, and vegetables cook rapidly over this natural heat source, with no visible flames and no fuel required beyond the Earth's internal energy. Diners at the adjacent restaurant can order meals prepared using this method, experiencing food cooked by geothermal heat accumulated and stored over centuries. The grill reaches temperatures that rival conventional ovens, yet the only input is the steady warmth rising from the volcanic rock.
This installation serves both as a scientific demonstration and a working kitchen, merging ancient volcanic knowledge with modern culinary practice. The efficiency of the grill shows how accessible geothermal energy is at Timanfaya; no pump, no circulation system, no complex technology is required. The heat simply flows upward continuously, year after year, a reliable source of energy that has never diminished since the hermit Hilario first encountered it.
200°
At a few metres below the surface, ground temperatures reach approximately 200°C.
Three Centuries of Retained Heat: The 1730s Eruptions
The foundation for all this heat is the eruption cycle that began in 1730 and lasted for six years, transforming Lanzarote's landscape entirely. Volcanic activity covered vast areas with lava fields, reshaped the coastline, and buried villages. More importantly for Islote de Hilario, it deposited molten material and heated rock at depths that have never fully cooled. Nearly 300 years later, the ground retains enough thermal energy to flash water to steam, ignite wood, and cook food without external fuel. This persistence of heat is one of the most striking aspects of volcanic geology.
The rock at depth cools slowly because it is insulated by layers of material above and surrounded by more warm rock on all sides. Heat loss occurs primarily through radiation and convection at the surface, a slow process when the temperature differential is extreme. Mathematical models of volcanic cooling suggest that such heat retention over three centuries is entirely consistent with the geology of the region. The 1730 eruptions deposited sufficient thermal mass that Timanfaya remains one of the hottest places on the planet just below the surface, in a region where air temperatures are moderate year-round.
Magma or Stored Heat: Understanding the Source
A common question is whether the heat at Islote de Hilario comes from active magma still rising from the Earth's mantle, or whether it is residual heat stored in rock since the 1730s eruptions. The evidence points clearly to stored heat rather than ongoing magma intrusion. If magma were actively rising, the temperature would be stable or increasing; instead, measurements over the past few decades show a slow, steady decline. The rock has not been replenished with fresh molten material in recent centuries. The system is cooling, albeit very slowly, from a state of extreme heating that began when lava was actively flowing.
The temperature gradient at Timanfaya also supports this interpretation. At depths of 30 metres, temperatures still exceed 100 degrees Celsius, but they decrease with further depth. If magma chambers were feeding heat from below, the deepest boreholes would show higher temperatures than the shallowest ones. Instead, the pattern is consistent with a body of heated rock gradually losing energy to the surrounding crust. This is not to say magma is absent from Lanzarote entirely; seismic monitoring confirms that volcanic systems remain active beneath the surface. But at Islote de Hilario specifically, the heat is ancient rather than active, a legacy of 1730.
Hilario the Hermit: Living with Volcanic Heat
The hermit Hilario remains a figure of legend and incomplete historical record, but his presence on this volcanic plateau in the 18th century is documented. He lived in isolation on the exposed ground, without modern shelter or tools, in a landscape that was actively transforming due to volcanic activity. His choice to remain, and the isolation he maintained for years, suggests either profound spiritual commitment or an unusual adaptation to extreme conditions. The geothermal phenomena at what is now called Islote de Hilario would have been familiar to him, perhaps even useful for survival in an otherwise barren landscape.
Local tradition holds that Hilario used the natural heat for warmth and cooking, drawing on resources that no other person in such isolation could have accessed. Whether or not these accounts are historically precise, they point to a reality: Timanfaya's heat is not merely a scientific curiosity but a usable energy source that has been accessible for centuries. The naming of Islote de Hilario honours both the hermit's presence and the geological marvel he inhabited. His solitary years on this plateau connect the human story to the volcanic story, reminding visitors that this landscape has always been extraordinary.
