Seafloor Spreading Rate Calculator

Seafloor Spreading Rate Calculator

Calculated Results:

Half-Spreading Rate: cm/year

Full Spreading Rate: cm/year

Note: Spreading rates vary globally, typically ranging from 1 cm to 16 cm per year.

function calculateSpreadingRate() { var distanceKm = document.getElementById("distanceInput").value; var ageMa = document.getElementById("ageInput").value; var resultArea = document.getElementById("resultArea"); var halfRateDisplay = document.getElementById("halfRateDisplay"); var fullRateDisplay = document.getElementById("fullRateDisplay"); if (distanceKm > 0 && ageMa > 0) { // Formula: Velocity = Distance / Time // Convert Distance: 1 km = 100,000 cm // Convert Time: 1 Ma = 1,000,000 years var distanceCm = distanceKm * 100000; var ageYears = ageMa * 1000000; // Rate in cm/year var halfRate = distanceCm / ageYears; var fullRate = halfRate * 2; halfRateDisplay.innerText = halfRate.toFixed(2); fullRateDisplay.innerText = fullRate.toFixed(2); resultArea.style.display = "block"; } else { alert("Please enter valid positive numbers for both distance and age."); } }

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Understanding Seafloor Spreading Rates

Seafloor spreading is a geological process where tectonic plates—large slabs of Earth's lithosphere—split apart from each other. This occurs at mid-ocean ridges, where new oceanic crust is formed through volcanic activity and then gradually moves away from the ridge.

How to Calculate Seafloor Spreading

The calculation of the seafloor spreading rate is a fundamental exercise in paleomagnetism and plate tectonics. Because we know that the Earth's magnetic field flips polarity at known intervals, geologists can use the magnetic "stripes" on the ocean floor to determine how old the crust is at a specific distance from the ridge.

The basic formula used is:

Rate (V) = Distance (d) / Time (t)

Units of Measurement

In geology, spreading rates are most commonly expressed in centimeters per year (cm/yr). This is because tectonic plates move roughly at the same speed that human fingernails grow. To calculate this using standard geological data, we must convert:

• Distance: Kilometers to Centimeters (1 km = 100,000 cm)
• Time: Millions of years (Ma) to Years (1 Ma = 1,000,000 years)

Half-Spreading vs. Full Spreading Rate

When you measure the distance from the central ridge to a specific point on one side, you are calculating the half-spreading rate. However, because the ridge is pushing plates in both directions simultaneously, the full spreading rate (the speed at which the two plates are moving away from each other) is double that value.

Realistic Examples

Region	Approx. Full Rate	Classification
Mid-Atlantic Ridge	2 – 5 cm/year	Slow-spreading
Southeast Indian Ridge	5 – 9 cm/year	Intermediate-spreading
East Pacific Rise	9 – 16 cm/year	Fast-spreading

Step-by-Step Calculation Example

Suppose you find a sample of basalt on the seafloor that is 200 km away from the ridge axis. Laboratory dating shows this rock is 10 million years old (10 Ma).

1. Convert distance to cm: 200 km × 100,000 = 20,000,000 cm.
2. Convert time to years: 10 Ma × 1,000,000 = 10,000,000 years.
3. Calculate Half-Rate: 20,000,000 / 10,000,000 = 2 cm/year.
4. Calculate Full-Rate: 2 cm/year × 2 = 4 cm/year.