I have a simple OpenGL program that renders terrain with a texture. It exhibits some strange behaviors (see video) that look similar to depth test issues. However, I have already enabled depth test. Where else can I look to solve this problem?

https://www.youtube.com/watch?v=WHTFa3tMSyQ

This is the relevant setup code

glEnable(GL_BLEND);
glEnable(GL_DEPTH_TEST);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

... VBO and texture setup ..

glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
glClearColor(0.0f, 0.0f, 0.0f, 1.0f);

projectionMatrix = glm::frustum(-2.0, 2.0, -2.0, 2.0, 1.0, 10000.0);

... rendering stuff ...

glFlush();
swapEGLBuffers();