Next steps

The GeoLaB project is divided into several project phases: with the decision on geological suitability, the site exploration phase is completed, followed by the planning and approval phase. Provided that approval is granted, this is followed by tunnel construction and a test operation phase, before the actual research operation is planned.

Planing and Permitting Phase

The exploratory phase has shown that the Tromm area is a suitable research site. However, a specific location has not yet been determined. Now, concrete planning for the rock laboratory is beginning, followed by an extensive permitting process. The parties involved are seeking a specific location for the access tunnel and planning the surface and underground infrastructure, tailored to local conditions. The GeoLaB team is designing all structures to minimize impacts on people and the environment. The large-scale monitoring program already underway to protect drinking water and groundwater will continue.

To this end, they are conducting further exploratory drilling and geophysical surveys. Information on these will be published here. Extensive permits are required. The permitting process is a multi-stage procedure under the Federal Mining Act (BbergG). Reviews and approvals are carried out by the Hessian Mining Authority.

Geophysics

In July and August 2026, geophysical surveys will be carried out in the Tromm area, as was already the case in November 2025. Specifically, these surveys will include electrical resistivity surveys and gravimetry. The measurements do not cause any noticeable effects or noise disturbance.
Electrical resistivity surveys are used to determine the electrical resistance or conductivity of the subsurface. These data provide a more detailed picture of the geological structures beneath the surface. For the surveys, several long cable lines will be installed: electrodes will be placed every 10 meters along approximately 18 kilometers of survey lines, and every 20 meters along a further 3.8 kilometers. The electrodes remain in the ground for only a few hours and are removed immediately after the measurements have been completed.
Gravimetric surveys provide information about the density distribution within the subsurface. Portable instruments are used to collect measurements at approximately 1,000 individual survey points.

These investigations add to the results of the first two survey campaigns. During those campaigns, the research team gained an initial understanding of the subsurface and identified geological and hydrogeological structures. In the current survey campaign, these structures are being examined in greater detail through a higher density of measurement points.

Exploration Phase (until April 2026)

Seismic truck in operation on the Tromm. © GFZ

Drilling site with sound barrier on the Tromm. © KIT

In the exploration phase, scientists or specialist companies commissioned by them conducted investigations in 2024 and 2025 in the areas of Wald-Michelbach, Grasellenbach and Rimbach. The goal was to answer the question: Is the area around the Tromm actually geologically suitable for the research laboratory? The results of all investigations have been summarized in a scientific site report. With the decision on geological suitability, the exploration phase has been completed.

Various investigations have been carried out and are planned, the approval of which will be applied for at the Hessian Mining Authority:

» Hydrological monitoring: Sampling and other measuring points relating to water for hydrogeological and hydrochemical data collection.

» Seismic monitoring: Passive monitoring of ground vibrations through seismometer measuring points.

» Seismics: Investigating the subsurface using sound waves generated by vibrations.

» Geophysical measurements: Additional surveys to determine, for example, the electrical and magnetic properties of the subsurface.

» Exploratory drilling: Drilling from the Tromm into greater depths to study the geological layers in more detail.

Seismics

In September 2025, our seismic team has conducted a second survey campaign on the Tromm. The measurements in the municipalities of Grasellenbach, Wald-Michelbach, and Rimbach took about two weeks. The Helmholtz Centre Potsdam – GFZ German Research Centre for Geosciences is a GeoLaB project partner and has planned this campaign. Implementation has been carried out by DMT Group from Essen, which has many years of experience in this field.

Before measurements began, the seismic team installed geophones along the survey line in the ground. In addition, the team placed geophones in the borehole, creating an even more detailed image of the subsurface. After the measurements, all geophones have been removed.

Here you can find all information on the 2025 seismic campaign in one place.
For the GeoLaB project, a seismic survey campaign was carried out on the Tromm in September 2024 in the municipalities of Grasellenbach, Wald-Michelbach, and Rimbach. The measurements lasted about two weeks. The survey was planned by GeoLaB project partner GFZ (Helmholtz Centre for Geosciences). The operational work was commissioned to DMT Group from Essen, a company with many years of experience in conducting seismic campaigns.

The method used was reflection seismics with vibration sources — a minimally invasive exploration technique for studying the upper Earth’s crust. Similar to medical ultrasound, waves are sent into the subsurface from the surface to image internal structures.

Information about the completed seismic survey campaign in September 2024 can also be found in the seismic survey flyer (german only).
Measurement Methods

Using sound waves generated by vibration, the subsurface geology is examined (seismic survey). Measuring devices (geophones) record the reflected waves.

MEASUREMENT METHODS
Reflection seismics is a geophysical method used to create an image of the upper Earth’s crust. The diagram illustrates how sound waves generated by a vibrator truck are sent into the ground. These waves travel through different geological layers and are reflected at their boundaries. At the surface, the reflected waves are recorded by geophones — instruments that detect weak ground vibrations. From the arrival time and properties of the returning echoes, a detailed image of the subsurface can be computed.

PROCESS
Before measurements begin, geophones are installed. For this, staff from DMT Group, supported by the GeoLaB team, place the devices into the ground along the survey line and remove them afterward. To generate the required sound waves, a so-called vibrator truck is used. This vehicle is equipped with vibrating plates that transmit sound waves into the ground.

Information about the completed seismic survey campaign in September 2024 can also be found in the seismic survey flyer (german only).

Seismic survey truck in operation on the Tromm. © GFZ

Geophysics

Research from the Air - for the energy of the future. At the end of May 2025, a helicopter took off over the Tromm region with a clear mission: to survey the subsurface of the Odenwald from the air. Flying at low altitude and using cutting-edge magnetic technology, the Earth’s interior was made visible.

What´s it about?

The GeoLaB research project explores the use of deep geothermal energy from crystalline rock. To make this possible, researchers need an accurate picture of the geological structure. One key puzzle piece comes from precise, airborne magnetic field measurements.

What does the helicopter measure?

It records natural variations in the Earth’s magnetic field — without any impact on the environment. The measurements are contactless, quiet, and completely safe for people, animals, buildings, and nature. No photos or video recordings are taken.

This is what research looks like from the air — with its distinctive nose-boom probe, the helicopter scans the Earth’s magnetic field for GeoLaB. © Neuwirth
As part of the first survey campaign, geophysics revealed geological features in some areas of the Tromm. With a second geophysical survey campaign, we investigated these features in more detail — for example, by studying a smaller area with a higher number of measurement points or by using longer geoelectric survey profiles.

Starting in summer 2025, specially trained experts carried out measurements for the GeoLaB project in two phases. These are part of the geophysical investigations on the Tromm, which extended over several months. Gravimetry, magnetics, and geoelectrics were applied along survey profiles in different parts of the region.

Phase 1 of the potential geophysics in the first half of 2025 was intended to provide a rough overview of where rock boundaries and fractures are located. In Phase 2, starting in November 2025, experts aim to obtain an area-wide, high-resolution image of the geophysical conditions in selected areas. From a scientific perspective, the exact transition between the Tromm pluton and the Buntsandstein in the geological fault zone is of particular interest.

Scientists from the Karlsruhe Institute of Technology (KIT), a GeoLaB project partner, have planned the campaign. It will be carried out by Geophysik GGD mbH and its partners — an experienced team with many years of practical expertise.

Permissions: To access and use paths, forest, and agricultural land, permission must be obtained from municipalities, HessenForst, other authorities, as well as private landowners and tenants. GeoLaB has commissioned IPS Informations & Planungsservice GmbH to obtain these permits.
From September to December 2024, various measurements were carried out on the Tromm for the GeoLaB project: gravimetry (gravity field measurements), magnetics, and geoelectrics were performed along six survey profiles. The campaign was planned by the GeoLaB project partner KIT (Karlsruhe Institute of Technology). The operational work was commissioned to Geophysik GGD mbH and its partners, who have many years of experience conducting such surveys.

The campaign has been completed. Detailed information about the completed survey can be found in this Geophysics Flyer (german only).
Measurement Methods

SURVEYING AND GRAVIMETRY
All measurement points are measured using a GPS (global positioning system) with high measurement accuracy. This enables precise determination of the positions and contributes to the improved interpretation of all other measurement data. Gravimetry measures changes in the Earth's gravitational field caused by density differences in the subsurface. A gravimeter is placed on the earth's surface and records minimal changes in gravity. By combining gravimetry and GPS, detailed maps of the density distribution underground can be created.

MAGNETICS
Magnetics is a geophysical method for measuring variations in the earth's magnetic field. These are caused by different magnetic properties of the ground and are measured with a magnetometer. The instrument is placed on the ground and measures for a few minutes to collect accurate data.

DC GEOELECTRICS
Geoelectrics is a method for investigating the electrical conductivity of the subsoil. An electric direct current (DC) is passed through the ground and the resulting voltage is measured. The electrical resistance of the subsoil is calculated from this. This method makes rocks and rock layers with different electrical properties visible. The illustration shows a typical geoelectric setup, where electrodes are connected to a measuring unit by a cable. Stainless steel spikes, serving as electrodes, are inserted by hand a few centimeters deep into the ground at regular intervals along the profile. The entire measuring process is controlled by software.

These methods, along with illustrations, are also presented in the Geophysics Flyer (german only) for the 2024 survey campaign.

Typical setup of a geoelectric survey with installed electrodes and connecting cables. © Terradat (UK) Limited

Exploratory Drilling

On the Tromm, deep drilling was carried out in order to examine the geological layers even more closely by means of exploratory drillings. The drilling site was located southwest of the nature play area on the Tromm. At the fenced drilling site, areas for machinery and storage areas were set up, as well as containers for office work and staff. The drilling site was enclosed by a 10-metre-high noise protection wall. This requirement set by the permitting authority serves optimal noise protection for residents as well as measures to combat African swine fever.

In this film, the GeoLaB team provides insights into the work of the exploration phase with the deep drillings.

After completion of the investigations around the two drillings, the construction site will be fully dismantled again.

Site plan of the GeoLaB-1 exploratory borehole southwest of the Tromm natural playground. © KIT, aerial photo Tromm Google Maps, 2024
Between December 2024 and the end of January 2025, the drilling site was set up. The borehole was drilled in February and March 2025 to a depth of about 500 meters with a diameter of 16 centimeters, operating around the clock (24/7).

To study the geological layers in detail, core samples with a diameter of about 10 cm were collected throughout the entire drilling process. After drilling, additional downhole measurements were carried out in April.

Who performed the drilling?

The Karlsruhe Institute of Technology (KIT) commissioned Daldrup & Söhne AG to carry out the drilling work.

What makes this borehole special?

It provides a direct, detailed look into the subsurface of the Tromm. The entire 500-meter core was recovered, examined, and is being further analyzed at KIT in Karlsruhe to better understand the geological composition.

What else was the borehole used for?

In addition to collecting rock cores, the borehole was used for further investigations and measurements over about two weeks to better characterize the subsurface.

First core from the GeoLaB-1 borehole on the Tromm © GeoLaB
Due to the promising results of the first drilling, a second exploratory drilling was carried out in June 2025 from the same drilling site. This allowed us to examine a larger area of the Tromm massif in detail.

The special feature of the second drilling: from the very beginning, the engineers deliberately deviated it — by about one degree per 15 metres. Thus, after 730 metres, it reached a final depth of about 580 metres — more than 370 metres away from the drilling site. With this angled trajectory, the researchers were able to investigate the rock over a larger area. This also increased the likelihood of encountering fractures in the rock, which are crucial for assessing the geological suitability of the Tromm for geothermal research. Another important piece of the puzzle in the overall picture of the Tromm.

Construction site with drilling rig © KIT
The exploratory drillings are not only important for a direct insight into the rock and the structure of the Tromm, but could also be used for geophysical measurements. For this purpose, sensors were installed directly in the borehole, providing important data from the subsurface.

Before these measurements could begin, the borehole had to be prepared. The existing borehole of the first drilling was cleared of cement residues. For this, the drilling rig was set up again – however, no new drilling took place. The measure served solely as the technical preparation for the measurements in the following weeks.

Next steps

Planing and Permitting Phase

Geophysics

Exploration Phase (until April 2026)

Second Seismic Survey Campaign September 2025

Seismic Survey Campaign September 2024

Seismic Survey

GeoLaB takes off! Helicopter Survey Flights Over the Tromm

Geophysic Survey Campaigne 2025

Geophysic Survey Campaigne 2024

Geophysical Investigations

Drilling site

First Exploration Borehole GLB-1 (Spring 2025)

Second Exploration Borehole GLB-2 (June 2025)

Measurements from the borehole