Geothermal Heat Flow Calculator
Free Geothermal heat flow Calculator for geology & geophysics. Enter variables to compute results with formulas and detailed steps.
Formula
q = k x (dT/dz)
Heat flow (q) in mW/m^2 equals the thermal conductivity (k) in W/(m*K) multiplied by the geothermal temperature gradient (dT/dz) in C/km. This is derived from Fourier's Law of heat conduction applied to vertical heat transfer through the Earth's crust.
Worked Examples
Example 1: Continental Heat Flow Calculation
Problem: A borehole shows a gradient of 30 C/km through granite with thermal conductivity of 3.0 W/(m*K). Calculate heat flow and temperature at 4 km depth (surface temp 12 C).
Solution: Heat flow q = k x gradient = 3.0 x 30 = 90 mW/m^2\nTemperature at 4 km = 12 + (30 x 4) = 132 C\nClassification: Elevated heat flow (thinned crust zone)\nThis gradient and temperature are suitable for geothermal exploration
Result: Heat flow: 90 mW/m^2 (Elevated) | Temp at 4 km: 132 C
Example 2: Geothermal Resource Assessment
Problem: An area of 500 km^2 has 100 mW/m^2 heat flow, gradient 40 C/km, conductivity 2.5 W/(m*K), surface temp 10 C at 5 km depth.
Solution: Temperature at 5 km = 10 + (40 x 5) = 210 C\nTotal heat = (100/1000) x (500 x 10^6) = 50,000 kW = 50 MW thermal\nRecoverable heat = rock density x specific heat x volume x deltaT x 2%\n= 2700 x 900 x (500e6 x 5000) x 200 x 0.02 = very large\nElectric potential at 10% efficiency = 5 MW
Result: 210 C at depth | 50 MW thermal | Significant geothermal potential
Frequently Asked Questions
What is geothermal heat flow?
Geothermal heat flow is the rate at which thermal energy from Earth's interior is transferred to the surface through conduction, convection, and radiation. It is measured in milliwatts per square meter and represents the outward flux of heat through the crust. The global average heat flow is approximately 87 milliwatts per square meter on continents and about 101 milliwatts per square meter through oceanic crust. This heat originates primarily from the radioactive decay of uranium, thorium, and potassium isotopes in the crust and mantle, along with residual heat from planetary formation. Heat flow measurements are fundamental to understanding crustal thermal structure, tectonic processes, volcanic activity, and assessing the viability of geothermal energy resources for power generation.
How is geothermal heat flow measured?
Geothermal heat flow is measured using Fourier's Law of heat conduction, which states that heat flux equals the product of the thermal conductivity of the rock and the geothermal temperature gradient. In practice, this requires two separate measurements. First, the temperature gradient is measured by lowering precision temperature sensors into boreholes and recording temperatures at multiple depths, typically at intervals of 10 to 50 meters. Second, rock core samples are collected from the same borehole, and their thermal conductivity is measured in a laboratory using a divided bar apparatus or needle probe method. The heat flow value is then calculated by multiplying these two quantities. Shallow measurements within 200 meters can be affected by groundwater flow, seasonal temperature variations, and topographic effects, requiring corrections.
What factors affect the geothermal temperature gradient?
The geothermal temperature gradient, which describes how quickly temperature increases with depth, is influenced by several geological factors. The average gradient is roughly 25 to 30 degrees Celsius per kilometer, but it varies enormously from less than 10 to over 100 degrees per kilometer. The primary controlling factor is heat flow from below, which is highest in tectonically active regions near plate boundaries, mid-ocean ridges, and volcanic hotspots. The thermal conductivity of the overlying rock matters greatly because insulating sedimentary rocks with low conductivity create steeper gradients than highly conductive crystalline basement rocks. The concentration of radioactive heat-producing elements in crustal rocks contributes additional heat from above. Groundwater circulation can redistribute heat, creating anomalously high or low gradients depending on flow direction.
What are the different types of geothermal energy resources?
Geothermal energy resources are classified into several categories based on temperature and geological setting. Hydrothermal resources are the most commonly exploited type, consisting of hot water or steam trapped in permeable rock formations at temperatures above 150 degrees Celsius, suitable for direct electricity generation. Enhanced Geothermal Systems involve engineering artificial reservoirs in hot dry rock by hydraulic fracturing to circulate water through naturally hot formations. Low-temperature geothermal resources below 90 degrees Celsius are used for direct heating applications including district heating, greenhouse agriculture, aquaculture, and industrial processes. Geopressured resources combine thermal energy with dissolved methane and hydraulic pressure in deep sedimentary basins. Ground-source heat pumps utilize the nearly constant shallow ground temperature for building heating and cooling without requiring high-temperature resources.
How is the heat index calculated?
The heat index combines air temperature and relative humidity to determine perceived temperature. The NWS uses a regression equation with nine terms. At 90F with 60% humidity, the heat index is about 100F. Heat index values above 105F indicate danger. Direct sunlight can add up to 15F to the heat index value.
Can I use Geothermal Heat Flow Calculator on a mobile device?
Yes. All calculators on NovaCalculator are fully responsive and work on smartphones, tablets, and desktops. The layout adapts automatically to your screen size.