Weird artifacts on heightmap

so i have this compute shader in glsl that creates a heightmap:

#version 450 core

layout (local_size_x = 16, local_size_y = 16) in;

layout (rgba32f, binding = 0) uniform image2D hMap;


uniform vec2 resolution;




float random (in vec2 st) {
    return fract(sin(dot(st.xy,
                         vec2(12.9898,78.233)))*
        43758.5453123);
}


float noise (in vec2 st) {
    vec2 i = floor(st);
    vec2 f = fract(st);

    // Four corners in 2D of a tile
    float a = random(i);
    float b = random(i + vec2(1.0, 0.0));
    float c = random(i + vec2(0.0, 1.0));
    float d = random(i + vec2(1.0, 1.0));

    vec2 u = f * f * (3.0 - 2.0 * f);



    return mix(a, b, u.x) +
            (c - a)* u.y * (1.0 - u.x) +
            (d - b) * u.x * u.y;
}

float fbm (in vec2 st) {

    float value = 0.0;
    float amplitude = 0.5;
    float frequency = 1.0;


    for (int i = 0; i < 16; i++) {
        value += amplitude * noise(st);
        st *= 2.0;
        amplitude *= 0.5;
    }
    return value;
}






void main() {
    ivec2 texel_coord = ivec2(gl_GlobalInvocationID.xy);

    if (texel_coord.x >= resolution.x || texel_coord.y >= resolution.y) {
        return;
    }

    vec2 uv = vec2(gl_GlobalInvocationID.xy) / resolution.xy ;

    float height = 0.0;


    height = fbm(uv * 2.0);

   

    imageStore(hMap, texel_coord, vec4(height, height, height, 1.0));

}

and i get the result in the attached image.