Status
Extinct
No eruptions in thousands of years.
Grensdalur Volcano: Geothermal Hiking near Hveragerði
An extinct volcano near Hveragerði with hiking trails through geothermal terrain, one of the most accessible volcanic areas from Reykjavik.
Region
South Iceland
Near Hveragerði. Easy access year-round.
Quick Answer
Grensdalur is an extinct volcanic system near the geothermal town of Hveragerði, just 45 minutes from Reykjavik. While the volcano itself is no longer active, the area is rich with geothermal features: hot springs, steam vents, and the Reykjadalur hot river. The hiking trails here pass through a landscape shaped by both ancient volcanic activity and ongoing geothermal processes.
Sources and page update
Updated: 2026-09-10
This page is for trip planning, not emergency guidance. Stay on marked trails near geothermal areas. Ground can be hot and unstable.
For sourcing standards and how to report an error, see the editorial policy.
Official sources to check
Best for
Hiking + geothermal
Trails with hot springs and steam vents.
Distance
~45 min from Reykjavik
Via Route 1 to Hveragerði.
What to Expect
- Extinct central volcano classification: part of an ancient volcanic system that ceased erupting thousands of years ago
- Now characterized by residual geothermal activity: hot springs, steam vents, and altered clay deposits
- Reykjadalur hot spring river: 3 km hike from Hveragerdi to a natural warm river for bathing (year-round)
- The 2008 magnitude 6.3 South Iceland earthquake created new hot springs and altered geothermal features visibly
- Well-marked hiking trails from Hveragerdi through green valleys with volcanic rock formations and hot springs
- Colorful geothermal clay deposits: reds, yellows, and whites from mineral alteration by volcanic gases
- Geological features include ancient lava flows, hyaloclastite formations, and eroded volcanic plugs
Nearby Attractions
- Hveragerði geothermal greenhouses
- Selfoss town and services
- Golden Circle day trip route
- Kerið volcanic crater lake
- Þingvellir National Park (UNESCO)
- Ölfusá river (Iceland's largest by volume)
How to Get There
- Drive Route 1 to Hveragerdi (~45 km from Reykjavik, approximately 40 minutes)
- Hiking trailheads for Reykjadalur and Grensdalur valley are signed from central Hveragerdi
- No 4WD required: paved road all the way; parking at trailheads is free
- Reykjadalur hot river hike: 3 km each way (6 km round trip, 2-3 hours total including bathing)
- Public bus service (Straeто Route 51) runs from Reykjavik to Hveragerdi; trailhead is walkable from bus stop
- One of the most accessible volcanic/geothermal hiking areas in Iceland; no guide required
Best Time to Visit
- Low elevation does not guarantee year-round trail access; follow current closures
- June to August: warmest months, longest days, best conditions for Reykjadalur river bathing
- Winter: trails may be icy, so bring microspikes; confirm whether the bathing route is open
- Spring (April-May): wildflowers begin to appear; trail less crowded than summer
- Weekday mornings are least crowded at Reykjadalur; summer weekends can be very busy
- Geothermal steam is more visible in cold weather
Old eruptions and present geothermal heat
The Smithsonian catalogue calls Grensdalur the Hveragerði volcanic system and places its last activity in the Pleistocene. It lists no known Holocene eruptions, while describing the geothermal features that provide heat to Hveragerði.
That distinction helps explain the landscape: hot springs are evidence of subsurface heat, not a recent eruption date. A geological-system name also does not specify a bathing route. Use the Reykjadalur walking guide for that separate destination and follow local closures around thermal ground.
Planning help
Grensdalur FAQs
Quick answers with safety notes where it matters.
Is Grensdalur extinct?
Smithsonian places its last activity in the Pleistocene and lists no known Holocene eruptions. Geothermal heat remains part of the Hveragerði landscape.
Can you hike at Grensdalur?
Yes, Grensdalur has good hiking trails accessible from Hveragerði. The trails pass through varied terrain including geothermal areas, green valleys, and volcanic formations. The area is suitable for day hikes of various lengths.
What geothermal features are near Grensdalur?
The Grensdalur area near Hveragerði is rich in geothermal activity, including hot springs, steam vents, and the famous Reykjadalur hot spring river where you can bathe in a naturally heated river.
How do you get to Grensdalur?
Grensdalur is easily accessible from Hveragerði, which is about 45 minutes from Reykjavik on Route 1. Hiking trails start from the town and lead into the Grensdalur valley. No 4x4 is required.
When is the best time to visit Grensdalur?
Summer (June–August) offers the best conditions with longer days and accessible trails. However, the area can be visited year-round as it is close to the Ring Road and at low elevation. Winter visits may have icy trails.
For a countrywide view of Iceland’s volcanic systems, explore our Iceland statistics.